Noise-like Pulses Research Articles

Generation of switchable rectangular pulsed cylindrical vector beams in a 1.7 µm mode-locking all-fiber laser

In this paper, we demonstrate the generation of switchable rectangular pulsed cylindrical vector beams in a 1.7 µm mode-locking all-fiber laser by nonlinear amplifying loop mirror for the first time. Based on the nonlinear amplifying loop mirror mode-locking technology and mode selection coupler, the rectangular pulsed CVBs can be achieved and switched repeatedly and easily between the dissipative soliton resonance and noise-like pulse states. Furthermore, with the increasing of pump power, the duration of dissipative soliton resonance and noise-like pulse increase from 1.76 ns to 6.36 ns and 1.15 ns to 3.95 ns, respectively. In the meanwhile, both the peak power of dissipative soliton resonance and noise-like pulse are all clamped at 6 W all the time, showing the independence of clamped peak power and pulse type. Our work not only broadens wavelength range of switchable rectangular pulse, but also provides a novel pulse profile application of cylindrical vector beams.

Noise‐Like Pulse Seeded Supercontinuum Generation: An In‐Depth Review For High‐Energy Flat Broadband Sources

AbstractAs the need for compact, cost‐effective, and reliable laser sources continues to rise, fiber lasers have gained widespread interest in science and technology. In recent years, passively mode‐locked fiber lasers (PMLFLs) have emerged as pivotal tools for generating ultrashort pulses, propelling advancements across various domains including communication, manufacturing, medicine, defense, and security. Amongst the various types of lasing states supported by a PMFL, the emphasis in this review is on the noise‐like pulses (NLP) and their potential applications in supercontinuum generation (SCG). Interestingly, the quasi‐stationary operation of the NLP envelope containing numerous chaotic sub‐pulses has facilitated relatively high energy and broad bandwidth compared to standard mode‐locked laser pulses. Moreover, the NLP generation goes beyond a specific cavity arrangement, the nature of mode‐locking or cavity dispersion. Therefore, through this review, the foremost aim is to report the differences in NLPs across various experimental settings reported so far and highlight the strategies beneficial for high‐energy and broadband NLP development directly from a fiber oscillator. Secondly, the application of NLP as a seed laser is examined to stimulate SCG in different types of fibers, underlining the improved supercontinuum characteristics over the conventional ultrashort pulse pumping schemes. Finally, the benefit of NLP‐seeded SCG for various bio‐medical and industrial applications are highlighted, thanks to the broader and flatter continuum achievable through compact experimental settings.

Conventional soliton and noise-like pulse emissions at 1.98μm utilizing tungsten trioxide as mode-locker

In this paper, we experimentally demonstrate the dual pulse emissions of conventional soliton (CS) and noise-like pulse (NLP) in thulium-holmium co-doped fiber laser using tungsten trioxide saturable absorber (WO3-SA). The CS pulse delivered 2[Formula: see text]ps width, centered at 1982.8[Formula: see text]nm. Increasing the pump power and alteration of polarization states switched the CS to the NLP regime with 1990.0[Formula: see text]nm central wavelength, 17.2[Formula: see text]nm spectral bandwidth, and 396[Formula: see text]fs spike width riding on top of a wide picosecond pulse pedestal in the time domain. This work suggests the capability of WO3-SA as a pulse initiator for future dual-source ultrashort pulses based on an all-fiber laser cavity design.

Study of complex instability in a Thulium-doped figure-eight fiber laser including a polarization-imbalanced NOLM with no polarization control.

This study proposes a Thulium-doped figure-eight (F8) fiber laser design to be used as a platform to explore complex dynamics in passively mode-locked fiber laser systems. The proposed scheme incorporates a polarization-imbalanced nonlinear optical loop mirror (PI-NOLM) without a polarizer in the ring section. The absence of a polarizer prevents controlling the polarization state at the PI-NOLM input, which in turn allows the PI-NOLM switching power to vary dynamically during the laser operation. This leads to an intermittent noise-like pulse (NLP) operation, which is affected by complex instability in the form of non-periodic Q-switched-like behavior. Using real-time time-domain mapping techniques, we get a deep insight into the laser intricate dynamics, which involves not only NLPs, but also solitons and quasi-continuous-wave components with their subtle interactions. This study highlights the importance of the PI-NOLM in F8 laser schemes for the study and understanding of complex dynamics in Thulium-doped fiber lasers, which have been less extensively studied compared to other rare-earth-doped lasers. Our findings will contribute to the optimization and design of advanced laser systems for various scientific and industrial applications.

Spatiotemporal dissipation dynamics: a route to high-beam-quality and high-peak-power spatiotemporal mode-locked fiber lasers

Spatiotemporal mode-locking (STML) opens a new avenue for implementing high-energy, high-peak-power mode-locked fiber oscillators. However, the compromised beam quality poses a critical limitation to their broader applications. This study presents a method for enhancing the beam quality of STML fiber lasers by employing spatiotemporal dissipation involving the quenching and reabsorption effects of multimode erbium-doped fibers. The proposed technique introduces spatiotemporal saturable absorption, achieving high beam quality without the stringent conditions required for Kerr beam self-cleaning (BSC). Integrating spatiotemporal dissipation with Kerr BSC, we demonstrate an all-anomalous-dispersion Er-doped STML fiber laser, which produces solitons with 6.7 nJ pulse energy (the intracavity solitons with 25.8 nJ pulse energy and >52.8kW peak power), sub-500 fs pulse duration, and beam quality with M x 2/M y 2=1.23/1.20. To our knowledge, it is a record peak power for 1.5 µm band soliton lasers. Additionally, the approach enables the generation of noise-like pulses with M x 2/M y 2=1.04/1.13. This work not only advances our understanding of spatiotemporal dissipation dynamics in STML fiber lasers, but also paves the way toward high-performance STML fiber lasers, rendering them very attractive for applications.

A Bidirectional Mode-Locked Fiber Laser for Asynchronous Noise-like Pulse Generation

A Bidirectional Mode-Locked Fiber Laser for Asynchronous Noise-like Pulse Generation

Generation of noise-like pulses in a linear-cavity Tm fiber mode-locked laser based on FMF saturable absorber

As a real saturable absorber (SA) based on the nonlinear multimode interference (NL-MMI) effect, the devices based on the few-mode fiber possess numerous exciting characteristics due to their all-fiber structure, straightforward manufacturing process. In this paper, by employing a SA with the SMF-FMF-SMF structure in a linear cavity, we demonstrate a stable mode-locked Tm-doped fiber laser. At the pump power of 1 W, a single noise-like pulse (NLP) with a pedestal pulse duration of 28 ps and coherent peak width of 0.77 ps is generated at a central wavelength of 1940 nm with a 3 dB bandwidth of 10.51 nm. The stable noise-like pulse can be sustained from the lasing pump threshold up to the maximum pump power of 2.2 W without experiencing pulse splitting. The experiment results in a peak average output power of 116 mW, along with a corresponding maximum pulse energy of 24.73 nJ at a repetition frequency of 4.69 MHz. The high stability of our fiber laser is confirmed by the signal-to-Noise Ratio (SNR) of 63 dB, and its enduring stability is additionally validated over an 8-hour period. The experimental findings suggest that the SMF-FMF-SMF structure has significant potential in the simple and robust all-fiber mode-locked lasers operating in the noise-like pulse regime.

Pulse-state switchable mode-locked Tm-doped fiber laser based on linear-cavity nonlinear polarization rotation

We present an experimental demonstration of a pulse-state switchable Tm-doped fiber laser, mode-locked using linear-cavity nonlinear polarization rotation (LNPR). Compared to previous LNPR lasers with free-space structures, our laser cavity employs an all-fiber design, which enhances the laser flexibility. The laser operates in three states within a large anomalous dispersion, including conventional soliton, multi-pulse, and noise-like pulse states. This research provides an effective solution for realizing a multifunctional Tm-doped fiber laser with a simple and stable configuration, making it both appealing and promising for various practical applications.

In-fiber waveguide-based mode-locker for generating diverse ultrafast pulses

The pursuit of an optimal mode-locker in nonlinear photonics is crucial for advancing high-performance laser technologies. Addressing the market demands and technical complexities in creating highly integrated and robust saturable absorbers, we present a femtosecond laser-inscribed in-fiber straight waveguide, seamlessly integrating a few-mode fiber segment into a single-mode fiber. This design reduces costs, simplifies fabrication, and enhances system integration and stability. As a saturable absorber, it enables nonlinear polarization rotation and multimode interference, which are essential for ultrafast pulse generation. It exhibits slight polarization-dependent loss and significant modulation depth, effectively inducing mode-locking. Based on the waveguide, 1.36 ps soliton pulses with a 2.9 nm bandwidth at a central wavelength of 1573 nm are initially achieved in an anomalous dispersion regime. Transitioning to the normal dispersion regime, at 190 mW pump power, the system produces Q-switched mode-locked pulses at 1574 nm. Increasing the pump power to 295 mW results in 712 fs noise-like pulses at 1572 nm, featuring an 8 nm bandwidth and 4.57 MHz repetition rate. This advancement in fiber lasers, facilitated by hybrid nonlinear effects in the waveguide, represents a significant milestone, promising for nonlinear optics and photonics due to its simplicity, cost-effectiveness, compactness, robustness, and high damage threshold.

Polarization‐Induced Buildup and Switching Mechanisms for Soliton Molecules Composed of Noise‐Like‐Pulse Transition States

AbstractBuildup and switching mechanisms of solitons in complex nonlinear systems are fundamentally important dynamical regimes. Using a novel strongly nonlinear optical system, including saturable absorber metal‐organic framework (MOF)‐253@Au and a polarization controller (PC), the work reveals a new buildup scenario for “soliton molecules (SMs)”, which includes a long‐duration stage dominated by the emergence of transient noise‐like pulses (NLPs) modes to withstand strong disturbances arising from “turbulence” and extreme nonlinearity in the optical cavity. The switching between SMs and NLPs is controlled by the cavity polarization state. The switching involves the spectral collapse, following spectral oscillations with a variable period, and self‐organization of NLPs, following energy overshoot. This switching mechanism applies to various patterns with single, paired, and clustered pulses. In the multi‐pulses stage, XPM (cross‐phase‐modulation)‐induced interactions between solitons facilitate a specific mode of energy exchange between them, proportional to interaction duration, ensuring pulse stability during and after state transitions. Systematic simulations reveal the effects of the PC's rotation angle and intra‐cavity nonlinearity on the periodic phase transitions between the different soliton states and accurately reproduce the experimentally observed buildup and switching mechanisms. These findings can enhance the fundamental study and points to potential uses in designing information encoding systems.

Watt-level ultra-flat wideband supercontinuum generation in GeO2 fiber by femtosecond pulse

The high-power ultra-flat supercontinuum (SC) sources play an important role in various fields. In this letter, we experimentally demonstrated an all-fiber, high-power, ultra-flat SC source in GeO2 highly nonlinear fiber (HNLF) pumped by a femtosecond fiber laser system. The system is mode-locked by a semiconductor saturable absorber mirror with an all-polarization-maintaining (PM) structure. Based on the technology of chirped pulse amplification, a maximum power of 3.12 W was realized with a repetition rate of 80 MHz at 1.56 μm, and the pulse duration was compressed to 124 fs in a segment of PM single-mode fiber. Furthermore, by optimizing the length of the HNLF, a wideband SC spectrum of nearly 700 nm was obtained at10 dB with a maximum power of 1.82 W, and the flatness of the spectrum was better than 5 dB in the range of 1600–2200 nm. We observed that the pulse evolved into a noise-like pulse with a narrowest pulse duration of 62 fs. Thanks to the all-PM structure of the fiber laser, the long-term stability of SC power was manifested with a relative fluctuation as low as 0.53 % over 6 h.

High-energy noise-like pulsing in a thulium/holmium co-doped fiber laser with watt-level average output power

A Thulium/Holmium co-doped fiber laser with high-energy noise-like rectangular pulses at the central wavelength of 1985 nm is experimentally demonstrated. The experimental setup is based on a 298-m long nonlinear optical loop mirror. By varying the pump power from 3 to 10 W, the noise-like rectangular pulse width can be tuned from 2.8 to 15.2 ns, respectively, and under a maximum pump power of 10 W, 1.45 W of average output power is obtained. The pulse repetition rate is 671 kHz. Consequently, highly energetic optical pulses with 2.16 µJ pulse energy and an estimated peak power of 142 W are achieved. To the best of our knowledge, these pulses, which are generated directly from the laser cavity, possess the highest average output power and pulse energy for noise-like pulse emission in the near 2 µm wavelength region. The proposed laser source has the most straightforward all-fiber cavity design that has been proposed for generating high-energy noise-like rectangular pulses, and as such has potential applications in scientific research and as a pump source for mid-infrared supercontinuum generation.

1.35 μJ, 5.33 W Noise-Like Pulse Emission From an All-Polarization Maintaining Holmium-Doped Fiber Laser System

1.35 μJ, 5.33 W Noise-Like Pulse Emission From an All-Polarization Maintaining Holmium-Doped Fiber Laser System

Relative intensity noise reduction for noise-like pulses based on synchronous intensity modulation

Extra-cavity synchronous intensity modulation is a straightforward and effective approach to suppress the full-bandwidth relative intensity noise (RIN) for noise-like pulse (NLP) fiber lasers. In this work, the picosecond NLPs are produced by a homemade Er/Yb co-doped mode-locked fiber laser and subsequent optimized by the synchronous intensity modulation device. The photodetector (PD) and electro-optical modulator (EOM) allow the real-time measurement and modulation for each optical pulse. A detailed description of key parameters for components is presented. The impact of DC bias voltage and RF signal amplitude on resulting RIN is experimentally investigated. We demonstrate a noteworthy reduction in RIN from 5.62% before synchronous intensity modulation to 1.91% afterward. Numerical investigations suggest that this method is potential to suppress RIN to below 1% under ideal conditions. The key factor in RIN reduction is correct operating region and high photoelectric-conversion linearity. The synchronous intensity modulation is an effective method to obtain low-RIN NLP laser sources, valuable for some practical applications.

All-polarization-maintaining passively mode-locked Ho-doped fiber laser oscillator and amplifier based on a nonlinear optical loop mirror

Our study reveals results from an all-polarization-maintaining Ho-doped fiber laser that is passively mode-locked, consisting of both an oscillator and an amplifier. A stable, self-starting, noise-like mode-locked pulse is achieved in the Ho-doped fiber laser oscillator based on a nonlinear optical loop mirror at a wavelength of 2.05 μm. The mode-locked oscillator achieves a peak output power of 20.2 mW, generating pulses with a duration of 284 ps and exhibiting a coherence peak at 690 fs. Moreover, with the use of Ho-doped fiber amplifier, the mode-locked pulse can reach a peak output of 1.05 W while maintaining a power stability of 1.43 % over the course of an hour. The highest pulse energy reaches approximately 333.6 nJ, which equates to a peak power of 1.18 kW. The polarization extinction ratio is approximately 24.9 dB.

Surface plasmonic Au nanoparticles assisted CuO nanorods for broadband diverse ultrafast pulse generation

In virtue of the local surface plasmon resonance (LSPR) properties of metal nanoparticles to enhance the nonlinear optical response of the material, we successfully embed small-size Au nanoparticles into CuO nanorods. Then, theoretical and experimental methods verify that the assistance of ultrafast plasma response enhances the light-matter interaction. The LSPR characteristics and evanescent field distribution of the Au-CuO saturable absorber on the tapered fiber are studied by the finite element simulation method (FEM). By utilizing the Z-scan technology and twin-balanced detector system, excellent nonlinear optical (NLO) properties of the Au-CuO nanorods are demonstrated. Subsequently, depending on the remarkable nonlinear saturable absorption effect of Au-CuO, multiple operating states such as Q-switched, conventional soliton, double-subpulse soliton cluster, and noise-like pulse mode-locking are achieved in the erbium-doped fiber ring cavity at 1.5 μm. In addition, dual-wavelength mode-locking pulses with the center wavelengths of 1031 nm and 1035 nm are realized in the ytterbium-doped fiber ring cavity. This work describes an effective strategy to improve the NLO properties of CuO nanorods and indicates the great potential of Au-CuO in pulsed fiber lasers, opening a path for its application in ultrafast photonics and optoelectronics.

Influence of black phosphorus structural variations for soliton and noise-like pulse generations in an erbium-doped fiber laser

We demonstrate black phosphorus (BP) with structural variations of layers (Ls) and quantum dots (QDs) blended with polydimethylsiloxane (PDMS) spin-coated tapered fiber as a light absorbing material for conventional soliton (CS) and noise-like pulse (NLP) generations. Interaction of the evanescent field leads BP materials to exhibit saturable absorption characteristics, with measured modulation depths of 3.50% and 2.12%, respectively. When integrated into an erbium-doped fiber laser cavity, both saturable absorbers (SAs) generated CS pulses initially with durations of 836 fs (BPLs/PDMS-SA) and 1.11 ps (BPQDs/PDMS-SA). At higher pump powers, the pulses switched to NLP with double-scale autocorrelation traces of 283 fs spike on 50 ps pedestal (BPLs/PDMS-SA) and 184 fs spike on 65 ps pedestal (BPQSs/PDMS-SA) due to the optical limiting properties of BP materials. These versatile findings facilitate the potential opportunities of BP-based photonic devices for next generation of ultrafast fiber laser technology with compact and dual functionality.

Wavelength tunable noise-like pulses in a hybrid mode-locked erbium-doped fiber laser

The study demonstrates a new type of laser that generates wavelength-tunable h-shaped noise-like pulses (NLPs). We incorporated the nonlinear polarization rotation (NPR) mechanism into a figure-eight erbium-doped hybrid mode-locked fiber laser based on the nonlinear amplifier loop mirror (NALM). Under an intra-cavity net dispersion of −5.535 ps2, the system produced NLPs with a maximum pulse duration of 24.54 ns, a maximum single energy of 19.96 nJ and a maximum output average power of 14.46 mW when the pump power was set to 543 mW. By adjusting the pump power and fine-tuning the polarization controller, the laser can output NLPs with tunable wavelengths ranging from 1560 to 1601 nm. The flexibility of wavelength-tunable techniques has potential applications in laser detection, high-energy physics experiments, and other fields, enriching the research framework of noise-like applications.

Pulsating dynamics of noise-like pulses in a fiber laser with nonlinear optical loop mirror

We experimentally investigate the nature of pulsating noise-like pulses (NLPs) in a fiber laser based on the nonlinear optical loop mirror. By adjusting the intra-cavity polarization, three types of pulsating NLPs can be obtained in the cavity. By utilizing the dispersive Fourier transformation technique, the real-time evolution dynamics of NLP pulsation have been investigated in detail. Different from the conventional pulsating behavior, the NLPs undergo remarkable and periodical variations in their width with slight changes in pulse peak powers during pulsation process. We speculate that the wavelength-dependent gain saturation is involved in the pulsating NLP evolution. Quasi-periodic energy oscillations are associated with cyclic generation and subsequent walkoff of wavelength-shifted components, resulting in the different pulsating dynamics of NLP. Moreover, during pulsation process, the NLP splitting could happen with the increasing of energy. All these findings will help to complement our understanding of NLP pulsation in a fiber laser.

Buildup of different emission regimes in a nonlinear polarization rotation modelocked all-fiber laser

We investigated experimentally and theoretically the buildup of light pulses in an erbium-doped sub-MHz all-fiber laser modelocked by nonlinear polarization rotation. We were able to study the buildup of two different emission regimes: standard solitons and noise-like pulses. In each case, we were able to determine the round-trips required to achieve a stable emission state. Temporal traces and optical spectra of single pulses were measured along the start-up transient of the laser. The experimental results were also confirmed by numerical simulations. Under the specific conditions of this laser, the soliton regime takes about 400 round-trips to reach single-pulse emission. In the noise-like pulse regime, it takes only 20 round-trips for the characteristics of noise-like pulses to show up; although a more steady-state emission is reached also at about 400 round-trips.