Noise-like Pulses Research Articles

Raman-scattering-assisted noise-like pulse generation in an all-PM NOLM-based mode-locked fiber laser core-pumped by a 978 nm fiber laser

Stable Raman-scattering-assisted noise-like pulse is experimentally demonstrated in an all polarization-maintaining ytterbium-doped ‘nine-shaped’ mode-locked fiber laser based on nonlinear optical loop mirror. The pump source is a self-made single mode 978 nm fiber laser with a maximum output power of 8.45 W. Different pulse states are investigated through dispersive Fourier transform technology. First and second order Raman pulses are generated effectively with only 7.2 m length large-mode-area fiber. Numerical simulation is conducted to investigate the effect of gain fiber length on output laser wavelength. The output spectrum ranges from 980 nm to 1175 nm, the short-wavelength edge almost extends to the 978 nm pump wavelength, which is benefitted from the core-pumping scheme providing extremely high population inversion for gain fiber, as well as the short length YDF of 0.2 m suppressing reabsorption of radiation laser. The polarization extinction ratio is experimentally measured by a spectral subtraction method to be larger than 28 dB at each wavelength between 1010 nm and 1120 nm.

Switching and transformation of multi-state solitons in a slightly normal dispersion mode-locked fiber laser

Passively mode locked fiber lasers are excellent platforms for soliton generation. Here, multi-state switchable behaviors in a slightly normal dispersion mode-locked fiber laser are experimentally demonstrated with an identical configuration. A saturable absorber based on single-wall carbon nanotube is served as mode-locking device and an intrinsic birefringence spectral filtering is employed as a tunable inline filter. Consequently, with properly modifying pumping powers and orientations of polarization controller paddles, the operation regimes of the proposed laser could be reversibly switched between dissipative solitons and amplifier similaritons, and the characteristics of intermediate states are recorded. Tunable dissipative solitons with a tuning range of 38 nm and noise-like pulses could also alternatively be generated. This multi-state behavior switching could be attributed to the strong filtering caused by the limited gain bandwidth under strong pump strength. The experimental observations of these multi-state switchable transitions may offer insight into the pulse regime dynamics in the near-zero dispersion region and offer flexibility in multi-functional designs of the laser configuration, which would enable innovations in nonlinear optics and its applications.

Mechanism of noise-like pulse in all-normal dispersion all-fiber laser based on nonlinear polarization rotation.

We investigate the mechanism of changing the polarization state to generate noise-like pulses (NLPs) in the all-normal dispersion (ANDi) all-fiber laser based on nonlinear polarization rotation (NPR). Numerical simulations show that the intracavity positive and negative feedback states change with the polarization state, the peak power of the pulse will be clamped when the negative feedback comes into play, thus facilitating the transition from dissipative soliton (DS) to NLP. Experimentally, the observation of wavelength switching and transition between DS and NLP by simply adjusting the polarization state matches the numerical simulation results. This study contributes to a deeper understanding of the mechanism for generating NLP by changing the intracavity polarization state in ANDi all-fiber lasers based on NPR and offers new possibilities for pulse-switchable light sources.

Ultra-flat and high-efficient mid-infrared supercontinuum generation in indium fluoride fiber

We demonstrate ultra-flat and high-efficient mid-infrared supercontinuum (MIR SC) generation in indium fluoride (InF3) fiber with output average power of 9.9 W, power conversion efficiency of 67.8 % and 3 dB-spectrum width of >1570 nm. It is pumped by amplified 2 μm noise-like pulses and generated in a piece of 10 m InF3 fiber with core diameters of 9.5 μm. The 2 μm noise-like pulses is realized by nonlinear amplifying loop mirror mode-locking technique and amplified by two-stage amplifiers with pulse repetition rate of 1.513 MHz and 3-dB pulse envelope width of 2.2 ns. To further increase efficiency, the InF3 fiber is spliced directly to the pigtail of main amplifier with 92.47 % coupling efficiency, which is in good agreement with 92 % theoretical result of fundamental-mode coupling efficiency. To the best of the authors’ knowledge, this work achieves the flattest (3 dB spectral coverage of 2120–3690 nm) and corresponding highest efficiency (67.8 %) in MIR SC seeded by 2 μm pulses.

976-nm pulse-type switchable all-fiber mode-locked laser based upon nonlinear multimode interference

A 976-nm pulse-type switchable mode-locked fiber laser is experimentally demonstrated, for the first time to our knowledge, with a single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure-based saturable absorber (SA). The GIMF is bent into a given state to strengthen its effect on establishing mode-locking. By adjusting the intra-cavity polarization controller, the switching between dissipative solitons (DSs) and noise-like pulses (NLPs) can be achieved. Meanwhile, we also realize a second harmonic mode-locking (HML) in the same laser cavity. The laser provides a solution to realize 976 nm mode-locking operation with a simple and low-cost configuration and can serve as a potential tool for various applications.

Stable watt-level mode-locked noise-like pulse from an all-PM fiber oscillator at 2 µm

Stable watt-level mode-locked noise-like pulse from an all-PM fiber oscillator at 2 µm

Coexistence of noise-like pulse and dark pulse in an Er/Yb co-doped fiber laser

Coexistence of noise-like pulse and dark pulse in an Er/Yb co-doped fiber laser

Dynamical diversity of noise-like pulse and soliton explosion in NL-MMI mode-locked Er fiber laser

Dynamical diversity of noise-like pulse and soliton explosion in NL-MMI mode-locked Er fiber laser

Observation of operation states and wavelength-switching in spatiotemporal mode-locked lasers

The construction and investigation of spatiotemporal mode-locked (STML) lasers offer us an opportunity to comprehend and analyze exceedingly intricate high-dimensional nonlinear physical phenomena that underlie diverse behaviors. While the exploration of coherent mode-locking, such as multimode solitons, has been progressing in depth, there remains a dearth of understanding regarding random pulses or extreme events within STML lasers. In this study, an STML laser was constructed and implemented with two operating regimes. The laser demonstrated mutual switching between noise-like pulses and dissipative soliton states, accompanied by corresponding changes in the output spectrum. The transition of the laser's output spectrum from a single wavelength to a synchronous dual-wavelength at noise-like pulses operation was observed for the first time, as far as we all know. These findings contribute to a deeper understanding of spatiotemporal mode-locked lasers.

All-multimode fiber spatiotemporal mode-locked figure-eight laser based on multimode gain fiber.

In this paper, we report for the first time on an all-multimode fiber spatiotemporal mode-locked figure-eight laser operating at 1.0µm. This laser utilizes a multimode gain fiber and a nonlinear amplifying loop mirror mechanism. It can generate mode-locked noise-like pulses at different central wavelengths. Additionally, we observed the presence of a multi-soliton state within the cavity by reducing intracavity gain. This study contributes to a broader investigation of various pulse phenomena in spatiotemporal mode-locked lasers and provides valuable insights into further exploring the evolution of spatiotemporal dynamics in such systems.

Narrow-bandwidth picosecond dissipative soliton resonance in an all-anomalous-dispersion Er/Yb co-doped fiber laser

First, it is numerically demonstrated that narrow-bandwidth picosecond dissipative soliton resonance (DSR) pulses can be obtained in the all-anomalous-dispersion Er/Yb co-doped fiber (EYDF) laser, which is based on the nonlinear polarization rotation (NPR) mode-locking and narrow-band spectral filtering. The generated DSR pulses are characterized by a central peak on top of a rectangular pedestal temporally and two high-intensity spectral sidebands with less than 0.6-nm bandwidth. Second, the impacts of several key cavity parameters on characteristics of DSR pulses are investigated. Particularly, a new phenomenon of periodic evolution of the DSR pulse, featuring alternated high and low peak powers with the round-trips, is discovered by tuning filter bandwidth or net-cavity dispersion. Multi-pulse dissipative soliton (DS) and noise-like pulse (NLP) are also observed in the fiber laser. Finally, a 22.3-ps DSR pulse with 287.5-W peak power can be further compressed to 4.3 ps with 1126.5-W peak power by the dispersion compensation. This work further enriches the DSR pulse dynamics in the anomalous-dispersion region and paves a way to realize narrow-bandwidth picosecond DSR pulse fiber lasers.

Switchable noise-like pulse generation in an all-polarization-maintaining thulium-doped fiber laser

In this paper, a tuning method based on temperature control of a piece of polarization-maintaining dispersion compensation fiber (PMDCF) is proposed in an all-polarization-maintaining (all-PM) thulium-doped fiber laser. The proposed tuning method simplifies the tuning parameter of the all-PM fiber laser, and various patterns of noise-like pulse (NLP) output can be realized only by adjusting the temperature of the PMDCF. The rectangular-shaped NLP, NLP bunches, the coexistence of rectangular-shaped NLP and NLP bunches, double rectangular-shaped NLP, and the switching between them are observed only through changing the temperature of the PMDCF, which helps to improve the research on the underlying physical mechanism of NLP. To the best of our knowledge, this is the first report of various patterns of NLP and their switching phenomena in an all-PM thulium-doped fiber laser.

976 nm noise-like pulse mode-locked fiber laser

976 nm noise-like pulse mode-locked fiber laser

All-fiber spatiotemporal mode-locked based on Mamyshev mechanism with high energy noise-like pulse generation at 1550 nm

Intermodal dispersion is the main problem restricting the establishment and stability of spatiotemporal mode-locking (STML) in the anomalous dispersion region. In the experiment, we employ the multimode Er-Yb double-clad fiber to carry out the multimode operation as a gain medium. The nonlinear multimode interference is used to enhance the mode coupling and spatial filtering in the cavity, achieve the purpose of suppressing the intermodal dispersion, and successfully realize the 1550 nm spatiotemporal noise-like solitons of Mamyshev oscillator based on the multimode gain fiber. The noise-like spatiotemporal soliton pulse energy reaches ∼171.29 nJ, and the corresponding peak power is ∼30.32 kW. The intermodal dispersion suppression based on nonlinear multimode interference performance makes this laser an attractive tool for practical applications.

Coherent pulse generation based on noise-like-pulse pumped Raman amplification

The coherent Raman pulse generation based on the noise-like-pulse (NLP) pumped Raman amplification is numerically investigated in the cases with weak and strong walk-off effects between the pump and Stokes pulses. In the former case, the amplified Stokes pulse suffers from the temporal and spectral distortions because the random time-varying intensity profile of the NLP can be transferred to the Stokes pulse through combined effects of cross-phase modulation (XPM), stimulated Raman scattering (SRS), and spontaneous Raman scattering. In the latter case, the heavily germanium-doped fiber with large normal dispersion is firstly used as the Raman gain medium to improve the walk-off effect and Raman gain. As a result, the Stokes pulse can be amplified undistorted and possess linear frequency chirp and conversion efficiency of up to 82.4 %. Further, it is important to note that the NLP-pumped Raman fiber laser based on the large normal dispersion fiber can generate the Stokes pulse with linear frequency chirp, narrow temporal duration, and dissipative-soliton-like spectrum with steep edges, even though the saturable absorber is not introduced into the Raman fiber cavity.

Noise-like pulses generation and its beam self-cleaning effect in an all-fiber multimode cavity with a figure-8 scheme

The beam profiles of multimode mode-locked fiber lasers are highly multimode, the speckled beam profiles limit their potential application. To improve the beam profiles of multimode mode-locked fiber lasers, we proposed an all-fiber figure-8 multimode cavity and experimentally demonstrated the generation of noise-like pulses (NLPs) and beam self-cleaning of NLPs in the cavity at 1.5 µm. The laser was mode locked by a nonlinear amplifying loop mirror, an Er/Yb co-doped fiber provided gain, and 50 m OM4 fiber introduced enough nonlinear phase shift difference. The scheme generated NLPs with 159 mW average power, 2.78 MHz repetition rate and 57.19 nJ pulse energy. The packet duration of the NLPs increased from 0.61 ns to 2.99 ns when the pump power was increased from 2 W to 9 W. Nonlinear beam self-cleaning with a near Gaussian beam profile output was achieved in the multimode fiber laser. The M2 was measured to be 2.41 at the pulse energy of 6.83 nJ. We also obtained spatiotemporal mode-locked pulses with 1.03 ps duration and speckled beam profiles. This is the first experimental demonstration of NLPs in multimode fiber lasers, and beam self-cleaning of NLPs was observed for the first time. The results enriched nonlinear dynamics in multimode fiber lasers.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

Accessible interferometric autocorrelator for noise-like pulses based on a Fabry-Perot cavity.

In this work, we develop experimentally a Fabry-Perot fiber optic interferometer applied to the measurement of autocorrelation of complex dynamic pulses generated by a figure-eight fiber laser. The principle is based in the superposition of multiple pulses, which requires two partially reflecting flat surfaces in parallel, resulting in a simple and compact autocorrelator design. The autocorrelation trace obtained exhibits a typical double-scaled structure for noise-like pulses (NLPs), with an ultrashort coherence spur on the order of 100 fs riding upon a broad pedestal of 120 ps. Finally, we show experimentally that the developed Fabry-Perot device is able to measure accurately the autocorrelation of NLPs, as confirmed by comparing the measurement with that of a conventional autocorrelator scheme based on a Michelson interferometer, with the additional advantages of a more compact setup and a much easier alignment procedure compared to the latter.

Noise-like pulse generation in 1.95 µm region using bulk α-alumina saturable absorber

This work presents a tapered fiber decorated with bulk α-alumina with 4.08% modulation depth and 21.67 MW/cm2 saturation intensity which was responsible to induce noise-like pulse (NLP) in an “eye-safe” wavelength region. The light-matter interaction within evanescent field of ultrathin tapered fiber established NLP in a ring configuration of thulium-doped fiber laser with a broad spectral bandwidth of 45 nm centered at 1948 nm wavelength. The NLP was emitted at 11.36 MHz repetition rate in a net anomalous laser cavity. The generated pulse had a maximum pulse energy of 2.46 nJ at 1587 mW pumping power. The robustness of the NLP performance was validated with 3 h stability test, which opens new possibilities for future research of this material in the wavelength of exceeding 1.9 μm.

Generation of noise-like pulse using nickel-based metal-organic framework saturable absorber

We experimentally demonstrate the generation of noise-like pulse (NLP) in an erbium-doped fiber laser using a metal-organic framework (MOF)-based saturable absorber. To fabricate the device, a tapered fiber was coated with MOF material, nickel 1,3,5-benzene-tricarboxylic acid (Ni-H3BTC) using a spin-coating method. The fabricated Ni-H3BTC-MOF saturable absorber exhibited 4.5% modulation depth and 30.3 MW/cm2 saturation intensity. A mode-locked erbium-doped fiber laser operated in the NLP regime was successfully achieved at 1564.90 nm central wavelength having 3-dB bandwidth of 19.96 nm, repetition rate of 9.02 MHz, and signal-to-noise ratio of 57.17 dB at 248 mW pump power. The characteristics of the NLP was confirmed by the spike width of 148 fs riding on a pedestal pulse duration of 26.67 ps. The estimated value of its damage threshold was experimented to be beyond 4.69 GW/cm2. These results infer that MOF-based saturable absorber can be an alternative material for the generation of ultrashort pulses.