Search Results (170)

We demonstrate a novel bidirectional mode-locked ultrafast fiber laser based on an asymmetric dual-cavity architecture that enables freely tunable repetition rate differentials at the kilohertz level, while maintaining inherent common-mode noise suppression through precision thermomechanical stabilization. Through cascaded amplification and nonlinear temporal compression, we obtained bidirectional pulse durations of 33.2 fs (clockwise) and 61.6 fs (counterclockwise), respectively. The developed source demonstrates exceptional capability for asynchronous optical sampling applications, particularly in enabling the compact implementation of real-time measurement systems such as terahertz time-domain spectroscopy (THz-TDS) systems. Full article

In this work, we report the formation of multiple mode-locking states in an Erbium/Ytterbium co-doped fiber laser, such as domain-wall (DW) dark pulses, high-order dark harmonic pulses, dissipative soliton resonance (DSR) pulses, and dual-wavelength h-shaped pulses. By increasing the pump power and adjusting the quarter-wave retarder (QWR) plates, we experimentally achieve 310th-order harmonic dark pulses. DSR pulses emerge at a pump power of 1.01 W and remain stable up to 9.07 W, reaching a maximum pulse width of 676 ns and a pulse energy of 1.608 µJ, while Dual-wavelength h-shaped pulses have a threshold of 1.42 W and maintain stability up to 9.07 W. Using a monochromator, we confirm that these h-shaped pulses result from the superposition of a soliton-like pulse and a DSR-like pulse, emitting at different wavelengths but locked in time. The fundamental repetition rate for dark pulsing, DSR, and h-shaped pulses is 321.34 kHz. This study provides new insights into complex pulse dynamics in fiber lasers and demonstrates the versatile emission regimes achievable through precise pump and polarization control. Full article

Utilizing the nonlinear effects of black phosphorus (BP), the self-starting threshold and noise performance were optimized in a figure-9 mode-locked fiber laser configuration. Experimental results demonstrate that a mode-locked pulse output with a spectral bandwidth of 8.2 nm, center wavelength of 1033.5 nm, and repetition rate of 42 MHz is obtained. Compared with single-mechanism mode-locked lasers, the self-starting mode-locked threshold is reduced by 100 mW. Regarding noise characteristics, the signal-to-noise ratio (SNR) is enhanced to 68.4 dB and the phase noise is reduced to −115.6 dBc/Hz at 1 MHz to 10 MHz frequency offsets. The root mean square (RMS) of the output power is optimized to 0.9% and phase noise jitter is reduced to 1.9%. This work proves a novel approach to tackle the challenges of high self-starting thresholds and instability in mode-locked lasers. Full article

A temperature-sensing scheme is realized by a passively mode-locked Yb-doped fiber laser based on the nonlinear optical loop mirror (NOLM). The ambient temperature can be measured by detecting the pulse repetition frequency of the mode-locked fiber laser by an oscilloscope. When the ambient temperature increases from −40 °C to 6 °C, the pulse repetition frequency decreases linearly with a temperature sensitivity of 72.548 Hz/°C. The experimental results prove the feasibility of the mode-locked laser sensor operating in a low-temperature environment. Full article

In this study, we have demonstrated an ultrafast Tm-doped fiber laser utilizing the nonlinear multimode interference (NL-MMI) effect, with a single mode fiber–grade index multimode fiber–single mode fiber (SMF-GIMF-SMF) structure serving as the saturable absorber (SA). In addition to stable pulses, mode-locked pulses with chaotic features can be obtained in this fiber laser, characterized by a high average output power and pulse energy, resembling noise-like pulses. By employing the time-stretch dispersive Fourier transform (TS-DFT) technology, it can be seen that the sub-pulses constituting these pulses exhibit noisy characteristics with random intensities and energies. Furthermore, the numerical simulations elucidate the corresponding generation mechanism and dynamic evolution. These findings significantly enhance the comprehension of pulse dynamics and offer novel insights into the technological development and application prospects of ultrafast fiber lasers. Full article

This article reviews the research progress of all-polarization-maintaining mode-locked fiber lasers. Owing to their excellent resistance to environmental interference and high stability, all-polarization-maintaining mode-locked fiber lasers hold significant application value in various fields, including industrial processing, communications, medical applications, and military applications. This article provides a detailed introduction to the structures, working principles, and performance characteristics of all-polarization-maintaining mode-locked fiber lasers based on different mode-locking mechanisms, such as SESAMs, two-dimensional materials, nonlinear polarization rotation, nonlinear optical loop mirrors, nonlinear amplifying loop mirrors, and figure-9 cavity. Additionally, this article discusses the challenges faced by all-polarization-maintaining mode-locked fiber lasers and their future development directions, including integration, miniaturization, multi-wavelength output, and the potential applications of new materials. Full article

Fiber-optic Fabry–Pérot (F–P) sensors offer significant potential for non-invasive hemodynamic monitoring, but existing sensing systems face limitations in multi-channel measurement capabilities and dynamic demodulation accuracy. This study introduces a sparse-frequency-scanning white-light interferometry (SFS-WLI) system with an adaptive mode-locked cross-correlation (MLCC) algorithm to address these challenges. The system leverages telecom-grade semiconductor lasers (191.2–196.15 THz sweep range, 50 GHz step) and a Fibonacci-optimized MLCC algorithm to achieve real-time cavity length demodulation at 5 kHz. Compared to normal MLCC algorithm, the Fibonacci-optimized algorithm reduces the number of computational iterations by 57 times while maintaining sub-nanometer resolution under dynamic perturbations. Experimental validation demonstrated a carotid–radial pulse wave velocity of 5.12 m/s in a healthy male volunteer. This work provides a scalable and cost-effective solution for cardiovascular monitoring with potential applications in point-of-care testing (POCT) and telemedicine. Full article

We propose and demonstrate a tunable femtosecond electro-optic optical frequency comb by shaping a continuous-wave seed laser in an all-fiber configuration. The seed laser, operating at 1.5 μm, is first cascade-phase-modulated and subsequently de-chirped to generate low-contrast pulses of approximately 8 ps at a repetition rate of 5.95 GHz. These pulses are then refined into clean, high-quality picosecond pulses using a Mamyshev regenerator. The generated source is further amplified using an erbium–ytterbium-doped fiber amplifier operating in a highly nonlinear regime, yielding output pulses compressed to around 470 fs. Tunable continuously across a 5.7~6 GHz range with a 1 MHz resolution, the picosecond pulses undergo nonlinear propagation in the final amplification stage, leading to output pulses that can be further compressed to a few hundred femtoseconds. By using a tunable bandpass filter, the center wavelength and spectral bandwidth can be flexibly tuned. This system eliminates the need for mode-locked cavities, simplifying conventional ultrafast electro-optic combs by relying solely on phase modulation, while delivering femtosecond pulses at multiple-gigahertz repetition rates. Full article

Quasi-one-dimensional (quasi-1D) transition metal chalcogenides (TMCs), a subclass of low-dimensional materials, have attracted significant attention due to their unique optical and electronic properties, making them promising candidates for nonlinear photonics. In this work, NbTe₄, a quasi-1D transition metal tetrachalcogenide, was synthesized and employed for the first time as a broadband saturable absorber (SA) for pulsed laser applications. The nonlinear optical (NLO) properties of NbTe₄ were systematically characterized at 1.0 μm, 2.0 μm, and 3.0 μm, revealing saturation intensities of 59.53 GW/cm², 14 GW/cm², and 6.8 MW/cm², with corresponding modulation depths of 17.4%, 5.3%, and 21.5%. Utilizing NbTe₄-SA, passively Q-switched (PQS) pulses were successfully generated in the 1.0 μm and 2.0 μm bands, achieving pulse durations of 86 ns and 2 μs, respectively. Furthermore, stable mode-locked operation was demonstrated in an Er-doped fluoride fiber laser at 3.0 μm, yielding a pulse duration of 19 ps. These results establish NbTe₄ as a highly promising broadband SA material for next-generation ultrafast photonic devices and pave the way for the development of other quasi-1D materials in nonlinear optics. Full article

Femtosecond fiber lasers are widely utilized across various fields and also serve as an ideal platform for studying soliton dynamics. Bound-state solitons, as a significant soliton dynamic phenomenon, attract widespread attention and research interest because of their potential applications in high-speed optical communication, all-optical information storage, quantum computing, optical switching, and high-resolution spectroscopy. We investigate the effects of pump power variations on the formation of mode-locked solitons and bound-state solitons in a femtosecond fiber laser with a Cr₂S₃ saturable absorber (SA) through numerical simulations while observing the transition, formation, and break-up process of bound soliton pulses. By optimizing the cavity structure and adjusting the net dispersion, the mode-locked soliton is obtained based on this SA. This is the narrowest solitons produced by this SA to date, exhibiting the smallest time-bandwidth product. Moreover, stable double-bound solitons and unique (2 + 1) triple-bound solitons are successfully obtained. The diverse bound-state solitons not only demonstrate the excellent nonlinear absorption properties of Cr₂S₃ as a saturable absorber but also expand the scope of applications for Cr₂S₃ saturable absorbers in fiber lasers. Full article

In the presented work, erbium fiber lasers operating in the pulsed mode with a nonlinear element containing a vanadium oxide saturable absorber are demonstrated. The structure of the saturable absorber is based on a segment of thinned silica fiber coated with a thin-film vanadium oxide by the method of metalorganic chemical vapor deposition. A fiber laser scheme is demonstrated that allows controlling the transmission of the internal cavity of the resonator during laser generation and deposition of a thin film. We have demonstrated a method for obtaining and annealing nanocoatings with laser generation control. We controlled the laser output parameters directly during the synthesis of the saturable absorber material. Vanadium oxides obtained in the work demonstrated the Mott–Paierls phase transition practically at room temperature. In this work, the optical characteristics of the output radiation of a fiber laser with a saturable absorber were measured. At temperatures above 70 °C, the coatings demonstrate a passive Q-switch with a repetition rate of 38 kHz and a pulse duration of 3.8 μs. At temperatures below the phase transition, a short-term mode-locking mode occurs. The transmission jump at a wavelength of about 1350 nm during structural rearrangement was 24%. For comparison, VO₂ nanopowder in a polydimethylsiloxane elastomer matrix was used as a saturable absorber material. The nanopowder modulator made it possible to obtain pulses with a frequency of 27 kHz and a duration of about 7.2 μs. Full article

We generate an ultrafast Airy beam with a mode-locked fiber laser. A diffractive optical element is placed inside the laser cavity and applies phase modulation on the pulses propagating in the cavity. The pulsed Airy beam is then obtained by Fourier transform of the first order diffracted beam of the diffractive optical element. The experimental results show that the beam profile and propagation characteristics of the laser pulses are consistent with the theoretical analysis. The pulsed Airy beam fiber laser we constructed has the advantages of compactness, easy integration, low cost, and high stability and robustness, which are of great significance for applications in industrial and other tough environments. Full article

We demonstrate a low-intensity-noise, nonlinear amplifying loop-mirror-based mode-locked fiber laser by optimizing the polarization of the non-reciprocal phase bias and the pump current. If the angle of the waveplate in the non-reciprocal phase bias to the polarization axis of a polarization-maintaining fiber is not carefully aligned, parasitic polarization is induced. The parasitic polarization affects the minimum pump power and dynamic range of pump power for mode-locking, the intensity noise, and the comb power. To reduce intensity noise, the angle of the waveplate for the non-reciprocal phase bias is adjusted, and then the pump power is adjusted. The waveplate angle minimizing the intensity noise maximizes the dynamic range of the pump power for mode-locking and output power. As a result, the relative intensity noise has been suppressed by more than 32 dB at 15 kHz Fourier frequency. The polarization extinction ratio at the non-reciprocal phase bias is critical since it can determine a cavity loss and quality factor of a laser oscillator. Therefore, the additional polarizers cannot improve the intensity noise once the angle is mismatched and the polarization extinction ratio is degraded. Full article

Graphene oxide (GO) and reduced graphene oxide (rGO) have emerged as robust materials in the development of SAs for erbium-doped fiber lasers (EDFLs). Their exceptional optical properties, such as broadband absorption and fast recovery times, make them ideal candidates for achieving ultrashort pulse operation in EDFLs. With its higher oxygen content, GO offers greater nonlinearity and a tunable absorption spectrum, while rGO, yielded through chemical reduction, exhibits enhanced electrical conductivity and higher saturable absorption. These properties facilitate the generation of ultrashort pulses in EDFLs, which are highly desired for various medical imaging, telecommunications, and material processing applications. This review paper comprehensively analyzes the advancements in GO and rGO SAs in the context of EDFLs for mode-locking and Q-switching applications. The performance of EDFLs utilizing GO and rGO SAs is critically evaluated, focusing on key parameters, such as modulation depth, pulse duration, repetition rate, average power, pulse energy, peak power, and signal-to-noise ratio. Additionally, this review delves into the various synthesis methods of GO and rGO thin film, highlighting their impact on the optical properties and performance of SAs. The discussion on techniques to integrate the SAs into laser cavities includes direct deposition of nanoparticles/thin-film-based SAs, tapered-fiber-based SAs, and D-shaped SAs. Furthermore, the paper explores the challenges encountered during the fabrication of ideal GO and rGO SAs, with issues related to uniformity, stability, and tunability, along with proposed solutions to address these challenges. The insights provided offer valuable guidance for future research aimed at enhancing the performance of EDFLs using GO/rGO SAs. Full article

Palladium (Pd) nanocubes, a type of metallic nanostructure, have demonstrated remarkable optoelectronic properties, garnering significant attention. However, their nonlinear optical characteristics and related device applications remain underexplored. In this study, we report the fabrication of a novel saturable absorber (SA) by depositing Pd nanocubes onto a D-shaped fiber (DF). The Pd nanocubes, with an average size of 12 nm, were synthesized and integrated with a DF, resulting in a highly robust SA with broadband saturable absorption characteristics. When incorporated into Er³⁺-doped laser cavities, the Pd-DF SA enabled the generation of ultrafast pulses with a central wavelength of 1560 nm, a corresponding repetition rate of 26.7 MHz, and a temporal width of 1.85 ps. Our findings highlight the strong potential of the Pd-DF device as a versatile SA for constructing high-energy ultrafast fiber lasers. Full article