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We investigate the propagation characteristics of two temporally separated soliton pulses with the same spectra, under the influence of stimulated Raman scattering, within a single-mode optical fiber. This analysis explores the behavior of the interacting solitons while propagating in different chalcogenide materials, exhibiting new features and promising prospects for soliton transmission in optical communication systems. Our study included all the interaction parameters constituting the nonlinear Schrödinger equation (NLSE). We have examined the relationship between the Kerr nonlinearity, interpulse and intrapulse Raman effects, and material-dependent collision length featuring a key aspect in logic design and phase control in mode-locking systems. We have also systematically shown the manifestation of the Raman response function from the Raman gain curve, which our mathematical model (the Lorentzian model) provides, that exhibits a near agreement with experimental data. Our findings reveal significant differences from the typical behavior of two-soliton interaction only due to Kerr nonlinearity. Furthermore, we have investigated the mechanism of the net energy transfer between the interacting solitons as an integral phenomenon involved in multiple soliton propagation. These results provide an insightful understanding of the associated nonlinear effects in high-power soliton transmission systems and are foreseen to possess the potential for designing advanced optical switches and mode-locked lasers. [ABSTRACT FROM AUTHOR]

In this paper, we numerically study the influence of saturable absorber parameters, namely, modulation depth, recovery time, and saturation energy, on the performance of an ultrafast fiber laser that is mode-locked by a hybrid scheme of a saturation absorber (SA) and a nonlinear polarization rotation (NPR). Maps of mode-locked states related to intracavity wave-plates are created to evaluate the operation of hybrid mode-locking under different modulation depths of the SA. Along with the improvement of modulation depth of the SA, the mode-locked pulse results from a combination effect of the SA and NPR. The numerical analysis reveals that the SA parameters can significantly impact the pulse profile, peak power, and operation state. Moreover, they can also impact the selection of NPR mode-locked points, resulting in variation in stable single pulse output. A higher modulation depth can suppress the unstable multiple pulses' operation and convert them into harmonic mode-locked pulses. The obtained results indicate that the selection of appropriate SA parameters can effectively improve the output characteristics of hybrid mode-locked fiber lasers. [ABSTRACT FROM AUTHOR]

A narrow linewidth hybrid integrated distributed Bragg reflector (DBR) laser platform operating at 2 μm wavelength region is demonstrated. The laser architecture comprises AlGaInAsSb/GaSb type-I quantum well reflective semiconductor optical amplifiers butt-coupled to a Si3N4 photonic integrated circuit (PIC), incorporating a narrow-band DBR. The DBR is realized with a long spiral-shaped waveguide structure with periodic circular posts placed adjacent to the waveguide. At room temperature operating conditions, the laser exhibits a maximum continuous wave output power of more than 17 mW for emission near 2 μm. Linewidth properties are analyzed with a heterodyne measurement technique, involving the mixing of the laser signal with a frequency comb phase-locked to an ultra-stable laser. The hybrid laser exhibits a narrow linewidth of ∼8 kHz in 1 ms timescale and ∼50 kHz in 10 ms timescale. [ABSTRACT FROM AUTHOR]

Optical frequency combs with equidistant frequency modes have revolutionized metrology and spectroscopy. The most widespread combs consist of periodic pulse trains generated by mode-locked lasers. However, it has recently been demonstrated that most semiconductor lasers based on Fabry–Pérot cavities, such as quantum well laser diodes, quantum cascade lasers, and quantum dot lasers, can enter an unconventional regime without traditional mode-locking mechanisms. The time-domain profile of these self-locked combs features a frequency-modulated (FM) wave with quasi-continuous-wave intensity and near-linear frequency chirp. The observation of the FM mode of operation in lasers with significantly different dynamics suggested that this mode is a fundamental operating state of semiconductor lasers, stemming from a deeper underlying mechanism. Thanks to recent theoretical and experimental advances, the origin of FM behavior has become clear. In this Perspective, we discuss the current status of FM combs in semiconductor lasers based on Fabry–Pérot cavities, focusing on their physical origin, modeling, characterization, bandwidth enhancement, and potential in future applications. [ABSTRACT FROM AUTHOR]

Soliton pulsations are ubiquitous feature of non‐stationary soliton dynamics in mode‐locked lasers and many other physical systems. To overcome difficulties related to a huge amount of necessary computations and low efficiency of traditional numerical methods in modeling the evolution of non‐stationary solitons, a two‐parallel bidirectional long short‐term memory recurrent neural network (TP‐Bi_LSTM RNN) is proposed, with the main objective to predict dynamics of vector‐soliton pulsations (VSPs) in various complex states, whose real‐time dynamics is verified by experiments. For two examples, viz., single‐ and bi‐periodic VSPs, with period‐21 and a combination of period‐3 and period‐43, the prediction results are better than provided by direct simulations – namely, deviations produced by the TP‐Bi_LSTM RNN results are 36% and 18% less than those provided by the simulations, respectively. This means that predicted results provided by the neural network are better than numerical simulations. Moreover, the prediction results for unstable VSP state with period‐9 indicate that the optimization of training sets and the number of training iterations are particularly important for the predictability. Besides, the scheme of coded information storage based on the TP‐Bi_LSTM RNN, instead of actual pulse signals, is realized too. The findings offer new applications of deep learning to ultrafast optics and information storage. [ABSTRACT FROM AUTHOR]

The resolution and above all the stability of the geodetic reference frames is crucially important when global change, such as the sea level rise is observed. In this context systematic errors are still presenting a significant challenge to the measurement techniques of space geodesy. In order to overcome this unfortunate situation for the satellite laser ranging technique, we have utilized the injection of a mode-locked laser to provide a stable low-noise link between the optical domain, where the measurements are carried out, and the microwave regime in which the station clock is defined. We obtained a considerably enhanced measurement delay stability by 10–20 ps over several days, albeit with some experimental challenges. The implementation of waveform scans required us to revisit the issue of target structure and intensity variation in satellite laser ranging. [ABSTRACT FROM AUTHOR]

Solid‐state lasers based on mode‐locked technology are widely studied for their strong ability of average or peak power scaling and wide wavelength coverage. However, it usually takes a long time and a lot of effort to manually align an ultrafast solid‐state laser to achieve laser emission and stable mode‐locking. Here, an approach based on intelligent human‐like algorithms is proposed for aligning a solid‐state ultrafast laser system. The intelligent system is based on multi‐algorithm fusion and can fully simulate the process of observation, analysis, decision, and action of an experienced experimenter in the adjustment of the laser alignment and mode‐locking. The intelligent adjustment starts from the state of no laser emission, adopts the neural network, the modified augmented random search (ARS) algorithm, random search, and sliding window strategy, and takes the fluorescence and speckle patterns as indications to realize the laser emission and stable mode‐locking automatically. Several validation experiments are conducted using this intelligent system, and the stable mode‐locked pulses can be achieved within 40 s. This technology provides an efficient solution to the ultrafast solid‐state laser that requires full automatic laser emitting and stable mode‐locking for the first time. [ABSTRACT FROM AUTHOR]

The Manakov model, a framework of coupled non-linear Schrödinger equations, reflects an essential integrable model in non-linear physics, particularly used to analyze soliton behavior and wave interactions in multiple physical realms such as optical theory and plasma physics. Its distinct integrability features make it a treasure trove for investigating complex interactions between wave propagation and non-linear systems. With an emphasis on the stochastic Manakov model, this research article explores the field of stochastic partial differential equations (SPDE). This writing aims to lower the cost and time frame for experiments by using particular integration approaches to generate a wide variety of optical solitons to satisfy the said model. We complete our thrust using two innovative approaches: the Unified Ricatti Equation Algorithm which depends on the Riccati equation and its special solutions, and the New Extended Auxiliary Equation Method which builds several, more general traveling wave solutions to nonlinear partial differential equations using a more straightforward and cohesive approach. The combination of these two not only improves our capability to handle complicated SPDEs but also provides fresh perspectives on how soliton structures and stochastic effects connect within the governing model. By employing these techniques, we obtain various solitary and traveling wave solutions, including dark, singular, and bright solitons. To ensure the validity of the results, the density, contour, 3D, and 2D profiles of various attained solutions are numerically generated by selecting appropriate values for several proposed framework parameters. The presence of multiplicative white noise does not propagate to other components; it just affects the phase portion of the solitons. Research conducted on the mentioned framework involving multiplicative white noise encounters significant applications in optical communication systems. By comprehending soliton behavior and effects, we can optimize the transmission of information in optical fibers, strengthen mode-locked lasers, and advance laser-based material handling. This exclusive blend of challenging model and methodologies led to the discovery of numerous unique soliton solutions and their corresponding behaviors. [ABSTRACT FROM AUTHOR]

This study demonstrates the potential of nickel-trimesic acid, a material from the metal-organic framework (MOF) family, as a real saturable absorber (SA) for stable passively mode-locked pulse generation in erbium-doped fiber laser (EDFL) and thulium-holmium co-doped fiber laser (THDFL) ring cavities. The fabricated SA has modulation depths of 4.10% and 2.01%, and saturation intensities of 24.50 MW/cm2 and 14.50 MW/cm2, characterized at 1.56 μm and 2.00 μm, respectively. For EDFL, the mode-locked pulse centered at 1591.06 nm lasing wavelength was emitted with 3.19 nm spectral bandwidth and 1026 fs pulse width. Meanwhile, for THDFL, the generated pulse of 1410 fs was realized at 1951.60 nm central wavelength and 2.73 nm spectral bandwidth. The maximum average output power of 22.48 mW and 72.15 mW were measured from the EDFL and THDFL cavities, respectively. No perceptible variation of the optical spectrum and pulse width over one hour duration was observed for both laser cavities that indicated stable mode-locked pulse laser systems. These results demonstrate excellent performance from the nickel MOF-based SA and require further exploration of MOF-based SAs to enhance pulse mode-locking characteristics. [ABSTRACT FROM AUTHOR]

We utilize a femtosecond laser-inscribed small-period long-period fiber grating (SP-LPFG) to induce a nonlinear polarization rotation (NPR) effect for mode-locking pulses in a normal dispersion erbium-doped fiber laser (EDFL). The SP-LPFG has a length of 2.5 mm and a period of 25 μm. At wavelengths of 1556 nm and 1561 nm, it exhibits polarization-dependent loss (PDL) values of 20 dB and 14.5 dB, respectively, sufficient to trigger the NPR mechanism. With the pump power increased to 500 mW, the laser achieves normal dispersion mode-locked pulses centered at 1575 nm in the L-band, with a 3 dB bandwidth of 1.35 nm and a pulse width of 1.61 ps. The radio frequency (RF) spectrum reveals an signal-to-noise ratio (SNR) of up to 63.6 dB, demonstrating the excellent stability of the laser operation. This SP-LPFG holds promising applications, paving the way for efficient, compact, and stable normal dispersion ultrafast fiber lasers. [ABSTRACT FROM AUTHOR]

The intrinsic non‐Hermiticity of photonic devices with tunable optical gain and loss makes them excellent platforms to explore and implement applications based on parity‐time symmetry, and a notable example is mode management in micro‐cavity lasers. Thus far, parity‐time‐symmetric lasers are fabricated via conventional top‐down etching processes, which are known to cause cavity sidewall roughness that is potentially detrimental to laser performance. Bottom‐up fabrication of parity‐time‐symmetric lasers, however, has seen limited success due to strict requirements on the uniformity of cavity morphology. Here, parity‐time‐symmetric lasing is demonstrated in coupled InP micro‐ring cavities grown directly by selective area epitaxy. With a facet engineering technique, ring laser cavities with a highly deterministic morphology are realized, enabling parity‐time‐symmetric laser designs. Furthermore, benefiting from the versatility and controllability of this bottom‐up process, lasing mode selectivity can be enhanced through coupling gap tuning and cavity shape engineering, leading to single‐mode lasing with a peak side mode suppression ratio exceeding 17 dB and a threefold single‐mode brightness enhancement compared to a single, uncoupled laser cavity. This work unlocks a lasing mode management strategy that is previously unavailable to bottom‐up laser cavities, which is a major step toward the realization of on‐chip, low‐loss, and single‐mode micro‐cavity lasers. [ABSTRACT FROM AUTHOR]

Optical frequency combs have revolutionized frequency metrology and spectroscopic measurements, enabling the most precise measurements of all physical quantities. However, precision frequency metrology heavily relies on mode‐locked laser combs, which are only directly available for a few selected near‐infrared wavelength ranges. Recently, a strong tendency emerged for combs in the mid‐infrared molecular fingerprint region. To this end, several methods for wavelength conversion have been proposed and demonstrated, which nevertheless cost a degradation of coherence properties. Here a first approach is presented toward measuring resulting phase noise fluctuations, exploiting the temporal resolution of the dispersive temporal interferometry (DTI) technique for experimentally unveiling the carrier‐envelope phase dynamics of a cw‐seeded femtosecond optical parametric amplifier (OPA). Particularly, it is experimentally demonstrated for the first time that unexpectedly low seed power levels suffice to exceed vacuum fluctuations by more than an order of magnitude, resulting in pulse‐to‐pulse phase fluctuations of 82 mrad at rather moderate cw seed levels of 8 mW. Additionally, a formula is provided that allows exact prediction of the experimentally observed noise levels. This study therefore provides new insight into the role of vacuum fluctuations in OPAs, which open up an avenue for coherent dual‐comb systems in the mid‐infrared and beyond. [ABSTRACT FROM AUTHOR]

Dynamic control of the optical properties of gold nanostructures is crucial for advancing photonics technologies spanning optical signal processing, on-chip light sources and optical computing. Despite recent advances in tunable plasmons in gold nanostructures, most studies are limited to the linear or static regime, leaving the dynamic manipulation of nonlinear optical properties unexplored. This study demonstrates the voltage-controlled Kerr nonlinear optical response of gold nanofilms via the electrothermal effect. By applying relatively low voltages (~10 V), the nonlinear absorption coefficient and refractive index are reduced by 40.4% and 33.1%, respectively, due to the increased damping coefficient of gold nanofilm. Furthermore, a voltage-controlled all-fiber gold nanofilm saturable absorber is fabricated and used in mode-locked fiber lasers, enabling reversible wavelength-tuning and operation regimes switching (e.g., mode-locking—Q-switched mode-locking). These findings advance the understanding of electrically controlled nonlinear optical responses in gold nanofilms and offer a flexible approach for controlling fiber laser operations. Here the authors demonstrate voltage-controlled nonlinear optical response of gold nanofilm via electrothermal effect. They fabricate a voltage-controlled saturable absorber for achieving wavelength-tunability/operation-regime switching in a fiber laser. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate an ultrafast diamond Raman laser at 1240 nm with a pulse repetition rate of 956.62 MHz, a pulse duration of 39.5 ps, and an average power of up to 3.3 W based on synchronous pumping. The pump source is an electrical-pulse-modulated picosecond pulsed laser at 1064 nm with a repetition rate of 239.16 MHz and a pulse duration of 65.4 ps. A quadrupling repetition rate of the Raman pulse is achieved by synchronously amplifying both the forward and backward Raman pulses and the amplified Raman pulse undergoing two round trips in the resonator within one pump pulse period. The compression ratio of the pulse duration from the pump to the Raman is 1.66. This work offers a convenient and efficient method to significantly enhance the repetition rate of ultrafast crystalline Raman lasers and proves that a non-coherent ultrafast pump pulsed laser can be converted to a coherent mode-locked ultrafast Raman pulsed laser based on Raman conversion. [ABSTRACT FROM AUTHOR]

Fiber mode-locked lasers are nonlinear optical systems that provide ultrashort pulses at high repetition rates. However, adjusting the cavity parameters is often a challenging task due to the intrinsic multistability of a laser system. Depending on the adjustment of the cavity parameters, the optical output may vary significantly, including Q-switching, single and multipulse, and harmonic mode-locked regimes. In this study, we demonstrate an experimental implementation of the Soft Actor–Critic algorithm for generating a harmonic mode-locked regime inside a state-of-the-art fiber laser with an ion-gated nanotube saturable absorber. The algorithm employs nontrivial strategies to achieve a guaranteed harmonic mode-locked regime with the highest order by effectively managing the pumping power of a laser system and the nonlinear transmission of a nanotube absorber. Our results demonstrate a robust and feasible machine-learning–based approach toward an automatic system for adjusting nonlinear optical systems with the presence of multistability phenomena. [ABSTRACT FROM AUTHOR]

Passively harmonic mode-locking has been experimentally demonstrated in an erbium-doped fiber laser with large normal dispersion using single-multi-single mode structure as artificial saturable absorber. By increasing the pump power under the same polarization setting, the mode-locking operation can switch from fundamental mode-locked to 5th order harmonic mode-locked. Highest repetition rate of 4.26 MHz (5th order harmonic) is observed, with pulse width and pulse energy ascertained at 290 fs and 3.0 nJ, respectively. Excellent signal-to-noise ratio (SNR) of above 50 dB is observed for all harmonic orders. The findings validated that SMS structure can be used to generate stable and switchable high order of harmonic mode-locked. The low-cost SMS fiber for harmonic mode-locked generation technique could lay the groundwork for future sustainable industrial growth. [ABSTRACT FROM AUTHOR]

This study introduces a compact, portable femtosecond fibre laser system designed for synchronization with SPring‐8 synchrotron X‐ray pulses in a uniform filling mode. Unlike traditional titanium–sapphire mode‐locked lasers, which are fixed installations, our system utilizes fibre laser technology to provide a practical alternative for time‐resolved spectroscopy, striking a balance between usability, portability and cost‐efficiency. Comprehensive evaluations, including pulse characterization, timing jitter and frequency stability tests revealed a centre wavelength of 1600 nm, a pulse energy of 4.5 nJ, a pulse duration of 35 fs with a timing jitter of less than 9 ps, confirming the suitability of the system for time‐resolved spectroscopic studies. This development enhances the feasibility of experiments that combine synchrotron X‐rays and laser pulses, offering significant scientific contributions by enabling more flexible and diverse research applications. [ABSTRACT FROM AUTHOR]

This paper explores the production of linearly polarized laser output in a diode-pumped Yb:YAG laser at various pumping coupling ratios. To investigate the polarization mode locking mechanism with various pump coupling ratios, variations in beat frequency and beam profiles associated with different polarization states were analyzed. The study confirmed that the emission of linearly polarized laser with different mode-matching coefficients results from the coherent superposition of two orthogonally polarized eigenmodes within the resonator. Importantly, the experiment showed that adjusting pump coupling ratios allows achieving linearly polarized emission. Notably, within a specific range, linearly polarized laser emission remains unaffected by pumping coupling ratios. Beam quality factor measurements reveal that the beam quality of linearly polarized laser, generated through coherent superposition, surpasses that of partially polarized laser, with all beam quality factors being less than 1.5. [ABSTRACT FROM AUTHOR]

We demonstrate an all-polarization-maintaining (PM) ytterbium (Yb)-doped fiber laser with a figure-of-9 structure to generate mode-locked pulses with high single pulse energy and high repetition frequency. By exploiting the nonlinear amplifying loop mirror, a stably self-started mode-locking is achieved with a spectrum bandwidth of 13 nm and a pulse duration of 4.53 ps. The fundamental frequency is 97.966 MHz at the maximum output power of 143 mW in single pulse mode-locked operation, corresponding to the single pulse energy is 1.46 nJ. The output pulses maintain both high repetition frequency and high single-pulse energy. This laser oscillator can be an ideal seed source for applications such as high-energy amplifiers. [ABSTRACT FROM AUTHOR]

Ultrafast vortex beams have significant scientific and practical value because of their unique phase properties in both the longitudinal and transverse modes, enabling multi‐dimensional quantum control of light fields. Directly generating watt‐level ultrafast vortex beams with large angular momentum has remained a major challenge due to the limitations of mode‐locked materials and existing spatiotemporal mode‐locking generation methods. In this study, quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films are prepared by an anti‐solvent method and employed for the first time in a mode‐locked resonator operating in free space. Utilizing the angle‐based non‐collinear pumping and frequency doubling techniques, the second‐order ultrafast green vortex beams with a power of up to 1.05 W and a duration of 373 ps are generated. Experimental findings demonstrate the strong nonlinear saturable absorption properties of quasi‐2D PEA2(CsPbBr3)n‐1PbBr4 perovskite films at high power levels, highlighting their considerable potential in ultrafast laser technology and nonlinear optics. [ABSTRACT FROM AUTHOR]

In recent years, 2D Cr2S3 has earned lots of attentions in the fields of photocatalysis and photodetector due to its outstanding environmental stability and high responsivity. However, up to now, the optical properties of 2D Cr2S3, especially the NLO properties of Cr2S3 have been rarely studied. In this work, the NLO properties of Cr2S3-nanoparticles in 1 μm have been investigated by using open-aperture (OA) Z-scan method. The nonlinear absorption coefficient (β), modulation depth and saturable intensity are measured to be -2.6 cm/GW, 11.5%, and 0.115 MW/cm2, respectively. Furthermore, by depositing Cr2S3 nanoparticles on a side-polished fiber and inserting into a ytterbium-doped fiber laser (YDFL) cavity, stable mode-locking laser and Q-switching laser with a pulse width of 10.2 ns and 2.95 µs are achieved, respectively. These results demonstrate that Cr2S3 is a promising saturable absorber (SA) for the fiber laser applications. [ABSTRACT FROM AUTHOR]

In this research work, the nonlinear Landau–Ginzburg–Higgs model under investigation on the base of auxiliary equation method. The nonlinear Landau–Ginzburg–Higgs equation mainly describe nonlinear wave propagation, categorizes wave velocity, and materializes several phenomena through the dispersive system. The secured optical soliton solutions are interested, more general and some novel in kink solitons, bright solitons, periodic singular solitons, anti-kink solitons and dark solitons. The physical structure of some explored solitons solutions are represented graphically as contour, 2D and 3D plots by utilizing the symbolic computational tool Mathematica. The secured soliton will be play important role to the investigation of nonlinear phenomena in the various domains of nonlinear sciences and engineering such as optical fibers, nonlinear dynamics, communication system, solitons wave theory, nonlinear optics, transmission system, electronic engineering and ocean engineering. The auxiliary equation method is a basic analytical, powerful, efficient approach for the investigation of optical soliton inside the nonlinear Landau–Ginzburg–Higgs equation and also other nonlinear equations. [ABSTRACT FROM AUTHOR]

Optoelectronic oscillators (OEOs), which have attracted extensive studies in the past decades, are high quality-factor optoelectronic feedback loops for generating various ultra-pure microwave signals. In essence, OEOs are also dissipative nonlinear systems with multiple timescale characteristics and abundant nonlinearities, which open the possibilities for exploring localized dissipative solitary waves. In this paper, we demonstrate a new-class temporal dissipative soliton, i.e., dissipative microwave photonic soliton molecule (DMPSM), in a dual-bandpass OEO. Both the numerical simulation and experiment are conducted to reveal the physical mechanism of DMPSM generation and to evaluate the characteristics of the generated DMPSM sequences. Unlike optical soliton molecules in mode-locked lasers, the formation of DMPSMs arises from the combined action of multiple timescale coupling, nonlinear bistability, and time-delayed feedback in the OEO cavity, where the soliton interval and number in a DMPSM can be well-controlled through varying the multiple timescale variables in the OEO cavity, and the repetition frequency of the DMPSMs can be tuned through changing that of the initially injected perturbation signal. Meanwhile, the generated DMPSM sequence performs with high stability and excellent coherence, which shows enormous application potentials in pulse radar detection, dense microwave comb generation, and neuromorphology. [ABSTRACT FROM AUTHOR]

An experimental and computational optical pump-probe model is constructed, which utilizes two ultrafast pump pulses within the repetition period of a mode-locked laser to generate electron spin polarization. This report focuses on the effects of resonant spin amplification induced by an infinite train of the two-pump pulses. The first pump pulse is used to generate ordinary resonant spin amplification spectra, while the second pump pulse is used to manipulate the generated spectra. This model gives control of the accumulation of spin polarized electrons along a magnetic field by selecting the temporal separation of the two-pump pulses. The computational model accurately predicts and agrees with the experimental results, which shows manipulation of resonant spin peaks that are no longer entirely dependent on the external magnetic field. This two-pump model and the associated manipulations of resonant spin peaks can be used as a platform to construct and conceptualize resonant spin amplification-based optospintronic devices and applications. [ABSTRACT FROM AUTHOR]

Femtosecond laser inscriptions in optical media current offer the most reliable optical technology for processing of transparent materials, among which is the laser micromachining technology. In this process, the nonlinearity of the transparent medium can be either intrinsic or induced by multiphoton ionization processes. In this work, a generic model is proposed to describe the dynamics of femtosecond laser inscription in transparent materials characterized by a saturable nonlinearity. The model takes into account multiphoton ionization processes that can induce an electron plasma of inhomogeneous density and electron diffusions. The mathematical model is represented by a one-dimensional complex Ginzburg–Landau equation with a generalized saturable nonlinearity term in addition to the residual nonlinearity related to multiphoton ionization processes, coupled to a rate equation for time evolution of the electron plasma density. Dynamical properties of the model are investigated focusing on the nonlinear regime, where the model equations are transformed into a set of coupled first-order nonlinear ordinary differential equations, which are solved numerically with the help of a sixth-order Runge–Kutta algorithm with a fixed time step. Simulations reveal that upon propagation, spatiotemporal profiles of the optical field and of the plasma density are periodic pulse trains, the repetition rates and amplitudes of which are increased with an increase of both the multiphoton ionization order and the saturable nonlinearity. When electron diffusions are taken into account, the system dynamics remains qualitatively unchanged; however, the electron plasma density gets strongly depleted, leaving almost unchanged the amplitude of pulses composing the femtosecond laser soliton crystals. [ABSTRACT FROM AUTHOR]

Mixed lead–tin halide perovskites, as highly sensitive materials in the near-infrared region, hold significant potential for optoelectronic device applications. Here, mixed lead–tin halide perovskite saturable absorbers (SAs) have been developed by coupling with the side-polished surfaces of the single-mode fibers and excellent saturable absorption effects of the mixed lead–tin halide perovskite SAs have been demonstrated in the near-infrared region. By constructing the in-gap site assisted carrier transfer mode, the saturation absorption process of the mixed lead–tin halide perovskite SAs can be well explained, in which defects as in-gap sites can help the photon-generated carriers transfer into the conduction band and promote the Pauli-blocking-induced absorption bleaching in the SA. Moreover, ytterbium-doped fiber lasers based on perovskite SAs have been fabricated, and mode-locked operations at 1040 nm are achieved using the mixed lead–tin halide perovskite SA, generating ultra-short pulses with a pulse width of 683 fs, 3 dB bandwidth of 4.88 nm, signal-to-noise ratio exceeding 49.74 dB, and a repetition rate of 3.74 MHz. Our findings demonstrate that the mixed lead–tin halide perovskite SAs have excellent optical modulation capability and promising applications in the field of ultrafast photonics. [ABSTRACT FROM AUTHOR]

On-chip generation of optical frequency combs using nonlinear ring resonators has enabled numerous applications of combs that were otherwise limited to mode-locked lasers. Nevertheless, on-chip frequency combs have relied predominantly on single-ring resonators. In this study, we experimentally demonstrate the generation of a novel class of frequency combs, the topological frequency combs, in a two-dimensional lattice of hundreds of ring resonators that hosts fabrication-robust topological edge states with linear dispersion. By pumping these edge states, we demonstrate the generation of a nested frequency comb that shows oscillation of multiple edge state resonances across ≈40 longitudinal modes and is spatially confined at the lattice edge. Our results provide an opportunity to explore the interplay between topological physics and nonlinear frequency comb generation in a commercially available nanophotonic platform. [ABSTRACT FROM AUTHOR]

Laser-based light detection and ranging (LIDAR) offers a powerful tool to real-timely map spatial information with exceptional accuracy and owns various applications ranging from industrial manufacturing, and remote sensing, to airborne and in-vehicle missions. Over the past two decades, the rapid advancements of optical frequency combs have ushered in a new era for LIDAR, promoting measurement precision to quantum noise limited level. For comb LIDAR systems, to further improve the comprehensive performances and reconcile inherent conflicts between speed, accuracy, and ambiguity range, innovative demodulation strategies become crucial. Here we report a dispersive Fourier transform (DFT) based LIDAR method utilizing phase-locked Vernier dual soliton laser combs. We demonstrate that after in-line pulse stretching, the delay of the flying pulses can be identified via the DFT-based spectral interferometry instead of temporal interferometry or pulse reconstruction. This enables absolute distance measurements with precision starting from 262 nm in single shot, to 2.8 nm after averaging 1.5 ms, in a non-ambiguity range over 1.7 km. Furthermore, our DFT-based LIDAR method distinctly demonstrates an ability to completely eliminate dead zones. Such an integration of frequency-resolved ultrafast analysis and dual-comb ranging technology may pave a way for the design of future LIDAR systems. Here the authors develop a dispersive Fourier transform (DFT) based LIDAR method utilizing phase-locked Vernier dual soliton laser combs and demonstrate improved precision in the measurements. [ABSTRACT FROM AUTHOR]

The use of femtosecond laser radiation pulses is a very important tool used for metals or cell ablation, structural changes of materials optical properties and many other applications. In this light, we investigate on the generation of continuous-waves solitary structures induced by the dynamics of laser radiation propagation in transparent media with passively mode-locked saturable absober. Thus, understanding the characteristic properties of the dynamics of laser radiations turns out to be a pertinent and important step towards the optimization of their uses, as well as enhancement of tecnology. Our model is characterized by a complex Ginzburg–Landau (CGL) equation with a strong nonlinearity. In full nonlinear regime, numerical simulations of the nonlinear equation revealed multi-periodic wave structures which turn out to be multi-pulse trains. When the number of photon K increases, an increase of the Saturation Power influences considerably the pulse train. The results clearly prove the existence of multi-pulse structures and bound-state solitons with strong nonlinearity on-like cubic-quintic and saturable nonlinearities. [ABSTRACT FROM AUTHOR]

Lasers of low-coherence have attracted the attention of researches since the first publications on this topic in the 1960s and up to the present time. Low-coherent quasi-continuous LD-pumped Nd:YVO4 and Nd:YAG lasers with ≈ 1 ms pulses of 1064 nm radiation at 10 Hz repetition rate and 21–47 W output power are reported. Spatial coherence of laser radiation was determined by the contrast C of speckle patterns, C = 0.02 - 0.1. These Nd-lasers optical efficiency is in the range 20%–50% (depending on the coherence level). The low coherence was obtained at multimode lasing in a plano-spherical resonator near its stability limit. Experimental data are commented on using the calculated dependences of the number of laser modes and the degree of coherence on resonator configurations and pump spot sizes. The achieved contrast values C < 0.03 are below the level of human perception and correspond to the level of spatial coherence typical for thermal sources of radiation. Possible applications of the developed low-coherent multimode Nd-lasers and directions for further research are discussed. [ABSTRACT FROM AUTHOR]

Ultrafast pulsed lasers are pivotal in advanced domains such as optical communications, optical metrology, all-optical sampling, optical frequency combs, laser ranging, and laser machining, where saturable absorbers (SAs) are crucial components. Various SAs based on two-dimensional (2D) materials have attracted great attention in recent years due to their low cost, high stability, large modulation depth, broadband absorption, and excellent optical nonlinearity. In this work, Bi2O2Te nanosheets (NSs) based SA with a saturation intensity of 20.6 MW/cm2 and a modulation depth of 2.2% was prepared by utilizing liquid phase exfoliation (LPE) technique, which was firstly applied to a passively mode-locked ytterbium-doped fiber laser (YDFL). The experiment results show that a sequence of dissipative soliton (DS) pulse train with a repetition frequency of 3.303 MHz was obtained at 1032.5 nm. The pulse duration, signal-to-noise ratio (SNR), and maximum peak power were 166 fs, 70 dB, 21 kW, respectively. The results not only underscore the potential of Bi2O2Te NSs-based SA for ultrafast photonics applications around 1 μm wavelength, but also open a way for further exploration of high-performance, all-fiber laser sources utilizing 2D materials. [ABSTRACT FROM AUTHOR]

Measurement device independent quantum key distribution (MDI QKD) has attracted growing attention for its immunity to attacks at the measurement unit, but its unique structure limits the secret key rate. Utilizing the wavelength division multiplexing (WDM) technique and reducing error rates are effective strategies for enhancing the secret key rate. Reducing error rates often requires active feedback control of wavelengths using precise external references. However, for a multiwavelength laser, employing multiple references to stabilize each wavelength output places stringent demands on these references and significantly increases system complexity. Here, we demonstrate a stable, wavelength-tunable multiwavelength laser with an output wavelength ranging from 1270 to 1610 nm. Through precise temperature control and stable drive current, we passively lock the laser wavelength, achieving remarkable wavelength stability. This significantly reduce the error rate, leading to an almost doubling of the secret key rate compared to previous experiments. Furthermore, the exceptional wavelength stability offered by our multiwavelength laser, combined with the WDM technique, has further boosted the secret key rate of MDI QKD. With a wide wavelength tuning range of 5.1 nm, our multiwavelength laser facilitates flexible operation across multiple dense wavelength division multiplexing channels. Coupled with high wavelength stability and multiple wavelength outputs simultaneously, this laser offers a promising solution for a high-rate MDI QKD system. [ABSTRACT FROM AUTHOR]

Soliton "molecules", i.e., bound states of two or several solitons, represent a fundamental concept, which manifests itself in various nonlinear systems. They are dynamically similar to chemical molecules, attracting great interest to fundamental studies and offering potential applications (such as multilevel encoding of optical data). Here, the study demonstrates a novel dichromatic soliton‐molecule compounds (DSMC) built as a hybrid bound state of multiple bound soliton pulses carried by two wavelengths in a fiber laser. The DSMCs are maintained by two different binding mechanisms, viz., the self‐phase modulation (SPM) interaction between temporal solitons at the same wavelength, mediated by their tails, and the cross‐phase modulation (XPM) interaction between solitons at different wavelengths. They also exhibit unique temporal and spectral vibration profiles. Both static DSMCs and ones with robust internal vibrations are generated experimentally in the fiber laser, and numerically as solutions of the corresponding dissipative nonlinear model. The findings reported here expand the concept of soliton molecules and further promote their similarity to chemical molecules. [ABSTRACT FROM AUTHOR]

The peculiar nonlinear optical responses of two-dimensional (2D) materials endow them highly attractive for photonics applications. This review systematically discusses the performance of pulsed lasers employing 2D materials as their modulation device. First, it is crucial to categorize 2D materials that can act as saturable absorbers, encompassing a range of substances such as Graphene, Black Phosphorus, Topological Insulators, MXene, and even heterojunction. Furthermore, a thorough investigation is conducted to analyze the performance indexes to study the nonlinear characteristics of 2D materials in the pulse generation. Especially, the focus is on the 1.5 μ m band ultrafast lasers utilizing 2D materials. This paper also provides a comprehensive analysis of the obstacles and prospects in 2D materials preparation, and their utilization in the pulse laser systems. [ABSTRACT FROM AUTHOR]

In this work, ultrafast Yb-doped fiber laser was realized using multi-layer palladium diselenide (PdSe2) film as the saturable absorber, which was prepared by simple selenization of palladium film deposited by magnetron sputtering method. The prepared polycrystalline PdSe2 film has a thickness of about 12 nm. At a pump power of 180 mW, the obtained mode-locked fiber laser based on the PdSe2 film has a central wavelength of 1063.75 nm, a pulse width of 615 ps, a repetition rate of 17.66 MHz, and an output power of 4.43 mW, respectively. These results indicate that PdSe2 has great potential in applications of ultrafast lasers. [ABSTRACT FROM AUTHOR]

In this research work, we extracted the variety of newly optical soliton solutions which describe the wave propagation in nonlinear low-pass electrical transmission lines model by utilizing the auxiliary equation method. The secured solitons solutions yield a variety of typical soliton shapes, including dark solitons, periodic singular optical solitons, combined bright and dark solitons, kink wave solitons, bright solitons, ant-kink wave solitons, and solitary waves. The physical structure of extracted soliton solutions visualized in three different graphically structures such as three-dimension, two-dimensional and contour plotting on the choices of some constant parameters by utilizing the numerical simulations. This study explored optical solitons, solitary wave solutions, exact solitons for improving the performance of nonlinear low-pass electrical transmission systems. It provides an overview of solitons, their relevance, and stability principles. It also presents the mathematical formulation of the nonlinear low-pass electrical transmission lines model and discusses its implications for signal propagation. The secured soliton solutions have many applications in engineering and science such as nonlinear optics, fiber optics, laser optics, nonlinear dynamics, ocean engineering, electronic engineering, electrical engineering, computing engineering, power engineering and several other different kinds of physical sciences. The whole study shows that the suggested method is more powerful, effective, simple, and strong for looking into different types of nonlinear models involve in nonlinear sciences and the engineering presentation field. [ABSTRACT FROM AUTHOR]

An all-fiber low-repetition-rate SESAM mode-locked fiber oscillator combined with a dispersion-managed active fiber loop produces a flexible GHz burst-mode laser source. The high-power output is then produced by amplifying the GHz burst-mode laser source using an all-fiber chirped-pulse amplification system. Then, the laser is compressed using a grating pair compressor; a maximum amplified power of 97 W is obtained. This results in a compressed high power of 82.07 W with a power stability RMS of 0.09% and beam quality better than 1.2. Accurate dispersion control allows for the production of a high-quality pulse duration of 265 fs. [ABSTRACT FROM AUTHOR]

Fibre lasers are distinct in that their optical train is decoupled from the environment, especially in the all-fibre format. The attractive side of this decoupling is the simplicity of maintenance (no need to align the cavity or keep the optical elements clean), but the flip side of this is the difficulty one encounters when trying to control the output parameters. The components used in all-fibre laser cavities are usually different from those of free-space laser cavities and require new approaches to control. Essentially, an important task emerges, i.e., research and development of all-fibre laser components able to adjust their parameters (ideally by electronic means) in order to tune key parameters of the output radiation—wavelength, output power, and so on. The present review analyses the existing methods of control over the output parameters of mode-locked all-fibre lasers. It is further noted that a method relying on several independently pumped active media may be promising in this regard. [ABSTRACT FROM AUTHOR]

The quality of pump pulse in few-mode-fiber Brillouin optical time domain reflectometry (FMF-BOTDR) is vital for the spontaneous Brillouin scattering of modes LP01 and LP11 because it is the comprehensive effect of the main laser linewidth and pulse width, which is firstly discussed as we know. Numerical and experimental analysis are made for the amplitude and linewidth distribution, corresponding to the signal–noise ratio (SNR) and frequency resolution in BOTDR, respectively. Simulation shows the linewidths and peak values of Brillouin scattering have the same tendency for the LP01 mode and LP11 mode when the laser linewidth is less than 1 MHz but decreases slowly until they are the same when the laser linewidth is wider than 1 MHz. With the pulse width widening, the Brillouin linewidths for LP01 and LP11 modes both decrease sharply, almost to the natural linewidth of fiber 41 MHz and 35 MHz. Experimental results show that the amplitude distribution for the LP01 mode is always larger than for the LP11 mode if the main laser has the same linewidth and the frequency fluctuation is at least 2 MHz with the fiber laser and LP11 mode. The above results could provide improved sensing resolution for FMF-BOTDR sensing system. [ABSTRACT FROM AUTHOR]

This study reports new types of passive mode-locked Er-doped fiber laser (EDFL) based on a segment of doped fiber saturable absorber (DFSA) with Tm/Ho-doped fiber (THDF), Yb-doped fiber (YDF), and Er-doped fiber (EDF). By employing THDF-SA, a bright pulse sequence with a fundamental repetition rate of 17.86 MHz was obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, and second-harmonic pulses, were obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in both polarization directions was verified. Furthermore, using EDF-SA and YDF-SA, dark pulses and dark–bright pulses were obtained. A comparison of the three experiments revealed that THDF-SA effectively reduces the mode-locked threshold and improves the average output power. Compared with bright pulses, dark pulses offer several advantages such as resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL can find broad application in long-distance transmission, precision measurement, and other fields. [ABSTRACT FROM AUTHOR]

A single crystal of organic NLO material, cytosinium maleate (CM) has been grown by slow solvent evaporation technique. The cell parameters and space group have been determined by single crystal X-ray diffraction (SCXRD) analysis. The crystalline nature of the material was confirmed by powder X-ray diffraction (PXRD) study. Optical transmittance of the crystal in the visible and NIR region was measured by UV–Vis-NIR spectral analysis. The lower cut-off wavelength exists at 196 nm with excellent transmission from 262 to 1100 nm. The absence of absorption in the visible region makes CM suitable for optoelectronic applications. The obtained minimum value of Urbach energy indicates good crystallinity of CM. Fourier transform infrared (FT-IR) and FT-Raman spectral technique establishes the presence of functional groups in the CM crystal. Existence of several vibrations of COO− ion indicates that a proton from the carboxylic group of maleic acid is transferred to the nitrogen atom of cytosine and is responsible for the existence of N–H...O hydrogen bond. This ensures the formation of the crystal. The proton and carbon environment of CM has been determined by nuclear magnetic resonance (NMR) spectral analysis. It reveals the formation N–H...O hydrogen bond between C4H6N3O+ cation and C4H3O4—anion. The third order NLO parameters such as nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third order NLO susceptibility (χ3) have been determined by Z-scan method. The value of χ3 is found to be 1.1898 × 10–7 esu and this large value of χ3 is due to the presence of hydrogen bond in the molecular structure of CM. The obtained open and closed aperture curve exposes that CM has saturable absorption and self-focusing nature. The observed characteristics find uses in remote sensing, laser Q-switching and laser mode locking applications. The recorded Photoluminescence (PL) spectrum reveals that the crystal was suitable for ultraviolet fluorescence emission. [ABSTRACT FROM AUTHOR]

In our work, a multi-layer topological insulator (TI) Bi2Se3 thin film was prepared by the chemical vapor deposition method (CVD), and its saturable absorption and damage characteristics were experimentally studied. The results show that when the wavelength is 1064 nm, the saturable absorption parameters of TI: Bi2Se3 film, including modulation depth αs, non-saturable loss αns, and saturation power intensity Isat, increase with the increase in film thickness, and the damage threshold is inversely proportional to the film thickness. The thicker the film layer, the lower the damage threshold. Among them, modulation depth αs is up to 51.2%, minimum non-saturable loss αns is 1.8%, maximum saturation power intensity Isat is 560.8 kW/cm2, and the damage threshold is up to 909 MW/cm2. The influence of the controllable thickness of TI: Bi2Se3 film on passive Q-switching and mode-locking performance of laser is discussed and analyzed when TI: Bi2Se3 film is prepared by the CVD method as a saturable absorber (SA). Finally, the performance of TI: Bi2Se3 thin film applied to nanosecond laser isolation at the 1064 nm band is simulated and analyzed. It has the natural advantage of polarization independence, and the maximum isolation can reach 16.4 dB. [ABSTRACT FROM AUTHOR]

Ultralow-noise microwaves are essential in a wide variety of scientific and technological applications, such as metrology, radars, and communications. Here, we propose and demonstrate a scheme for generating an ultralow-noise microwave signal using a Brillouin optical frequency comb (OFC), which is based on the stimulated Brillouin scattering in combination with a frequency-shifted optical injection locking mechanism. The generated two intra-cavity Brillouin lasers are used as the intra-cavity pump for the eventual formation of the OFC and thus the microwave signal via the cascaded four-wave mixing process. Exploiting the cascaded narrowing effect in the Brillouin cavity assisted by the frequency-shifted optical injection locking, the proposed microwave signal source exhibits ultralow phase noise. Experimental results show that the phase noise of the microwave signal is equivalent to below −115 dBc / Hz for a 200-GHz carrier at 10 kHz offset. The system can work in stable operation without the need for any active feedback loop. [ABSTRACT FROM AUTHOR]

The internal flow of a pump turbine is unstable in part-load pump mode for small guide-vane openings, and the strong vibration caused by pressure pulsation is related to the safe and stable operation of the unit. A pump turbine with a six-splitter-blade runner was chosen for unsteady simulation analyses. A standard k-epsilon turbulence model was adopted to study the unsteady flow and pressure pulsation in part-load pump mode. The predicted results show that the flow in the draft tube and the runner with splitter blades was relatively stable and the flow of the blade-to-blade channel was symmetrical. When the inlet and outlet velocity distribution of the vanes was not uniform, a vortex began to form in the stay-vane domain. The reason for this vortex formation is explained, and it is pointed out that the existence of the vortex and backflow leads to uneven velocity distribution. The unsteady calculation results showed that the pressure-pulsation peak-to-peak amplitudes in the vaneless area and guide vanes were much higher than those of other monitor points because of rotor–stator interference between the rotating runner and the vanes. In addition, the pulsation characteristics of the monitor points at different circumferential positions in the vaneless region were quite different. In the vaneless area, the velocity gradient along the circumferential direction was very large, and there was a phenomenon of backflow. Also, the pressure pulsation was 0.2 times that of the runner rotational frequency, and the blade-passing frequency was a third-order frequency. At the outlet of the guide vane, the pressure pulsation was mainly of a low frequency with a complex vortex flow. Finally, the pressure pulsation began to decrease rapidly in the stay-vane region. [ABSTRACT FROM AUTHOR]

Optical microcomb underpins a wide range of applications from communication, metrology, to sensing. Although extensively explored in recent years, challenges remain in key aspects of microcomb such as complex soliton initialization, low power efficiency, and limited comb reconfigurability. Here we present an on-chip microcomb laser to address these key challenges. Realized with integration between III and V gain chip and a thin-film lithium niobate (TFLN) photonic integrated circuit (PIC), the laser directly emits mode-locked microcomb on demand with robust turnkey operation inherently built in, with individual comb linewidth down to 600 Hz, whole-comb frequency tuning rate exceeding 2.4 × 1017 Hz/s, and 100% utilization of optical power fully contributing to comb generation. The demonstrated approach unifies architecture and operation simplicity, electro-optic reconfigurability, high-speed tunability, and multifunctional capability enabled by TFLN PIC, opening up a great avenue towards on-demand generation of mode-locked microcomb that is of great potential for broad applications. Here the authors demonstrate a laser system that can directly output soliton microcombs, with high power efficiency and reconfigurability, paving the way for communication, computing, and metrology based on integrated photonics. [ABSTRACT FROM AUTHOR]

In the domain of continuous variable quantum key distribution (CV-QKD), a significant challenge arises in achieving precise frequency synchronization, an issue commonly termed as frequency locking. This involves matching the optical frequencies of both the quantum signal laser and the local oscillator laser for accurate symbol demodulation during the exchange of quantum keys. As such, implementations today still grapple with maintaining precise synchronization between sender and receiver frequencies, occasionally hindering the efficiency and reliability of the information exchange. Addressing this challenge, we present and empirically validate a novel approach to CV-QKD by incorporating a pilot tone-assisted frequency locking algorithm to enhance stability when using a locally generated local oscillator (LLO) at the receiver. The proposed design leverages software-based optimization techniques, thereby eliminating the need for high-speed electronic stabilization devices and achieving efficient performance at typical repetition rates. Specifically, the introduction of the pilot tone algorithm allows us to effectively mitigate phase fluctuations and preserve the integrity of the quantum signals during transmission without resorting to time-multiplexed reference pulses or fast-locking electronics in the lasers. Our results suggest the potential for achieving secure key rates of up to 1 Mb/s over a 50 km single-mode fiber when using these techniques, offering promising insights into the feasibility of high-rate, low-complexity CV-QKD implementations under realistic conditions. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of mode-locking in a laser with high-order transverse mode is important for achieving an ultrashort pulses train under more complicated conditions. So far, mode-locking with high-order transverse mode has not been reported in other lasers except the multimode fiber laser. This paper demonstrates robust mode-locking with high-order transverse mode in a Kerr-lens mode-locked vertical-external-cavity surface-emitting laser for the first time, to the best of our knowledge. While the longitudinal modes are locked, continuous mode-locking accompanied by high-order transverse mode up to TEM40 is observed. The threshold of the mode-locking is only a little bigger than that of the lasing. After the laser oscillation is built up, the mode-locked pulse train can be obtained almost immediately and maintained until the thermal rollover of the laser. Output powers of 717 mW under fundamental mode and 666 mW under high-order transverse mode are achieved with a 4.3 ps pulse duration and 1.1 GHz pulses repetition rate, and some phenomenological explanations to the related characteristics of the mode-locked operation of high-order transverse mode in the vertical-external-cavity surface-emitting laser are proposed. [ABSTRACT FROM AUTHOR]