Mode-locked Tm-doped Fiber Laser Research Articles

Uni-and bidirectional soliton rains in a NALM mode-locked Tm-doped fiber laser

We report the generation of different drifting patterns of soliton rains in a Tm-doped fiber laser mode locked by the technique of nonlinear amplifying loop mirror. The directional control of drifting soliton rain has been achieved by varying pump power and polarization. At a stable pumping level, a kind of bidirectional soliton rain is observed from a unidirectional one for the first time. In the bidirectional case, the forward and backward solitons, leaving from the two sides of the condensed phase, appear in the spectrum as two typical soliton peaks on a wide pedestal, 2 nm in separation. The spectral result implies that the secondary drifting solitons are formed by developing one strong sideband of the primary soliton rain, induced by a shift of the transmission peak.

Bismuth oxysulfide nanosheets as a novel saturable absorber for Er-doped and Tm-doped ultrafast fiber lasers

Novel layered bismuth oxysulfide (Bi2O2S) has shown great potential in photoelectric detection, photocatalysis, and photochemical cells due to its excellent properties such as excellent environmental stability, high carrier mobility, and favorite band gap (about 1∼1.5 eV). These excellent physical properties also make it advantageous for applications in the field of ultrafast photonics. However, to date, there has been no reported research on Bi2O2S in ultrafast fiber lasers. In this work, we report a facile method to synthesize Bi2O2S nanosheets by a combination of the hydrothermal and liquid-phase exfoliation (LPE) methods with good crystallinity and thickness less than 10 nm. Further, stable mode-locked pulses are achieved by applying the Bi2O2S SA in Er-doped and Tm-doped fiber lasers, respectively. The Er-doped mode-locked fiber laser has a pulse width of 453.6 fs and the optical spectrum is stable, with a maximum output power of 5.1 mW in the mode-locked state. The obtained Tm-doped mode-locked fiber laser based on Bi2O2S has an estimated pulse width of 2.69 ps and a maximum output power of 7.13 mW. Our results provide new opportunities for the development of Bi2O2S together with its application in ultrafast photonics.

Numerical investigation on influence of the saturable absorber in Tm-doped fiber laser

Here we numerically simulate the effect of the saturable absorber (SA) on the output performance of a Tm-doped mode-locked fiber laser in the anomalous dispersion regime. In particular, we analyze the effects of variations in recovery time, modulation depth, nonsaturable loss, and saturable energy on the parameters of the output pulse, such as pulse width and spectral bandwidth. It is demonstrated that the output pulse becomes unstable and broken when the SA recovery time is set below a crucial value. In addition, we demonstrate that the recovery time for stable conventional soliton pulse generation lies within a certain range that is sensitive to the cavity dispersion and modulation depth of the SA. These findings have significant implications for fiber laser design and our understanding of the SA effect at mid-infrared wavelength.

All-Polarization-Maintaining Figure-9 Mode-Locked Tm-Doped Fiber Laser With Amplitude Noise and Timing Jitter Suppression

An all-polarization-maintaining (PM) figure-9 mode-locked Tm-doped fiber laser that leverages a nonlinear amplifying loop mirror (NALM) incorporated with a chirped fiber Bragg grating (CFBG) for dispersion management is experimentally demonstrated. A dual output is obtained at the transmission and reflection arm of the NLAM loop, with a center wavelength of 1950 nm and 3 dB bandwidth of, respectively, 8.6 nm and 30 nm. The corresponding pulse repetition rate is 30.6 MHz with an average power of, respectively, 6.5 mW and 2 mW for the two outputted pulses. By utilizing an extra-cavity amplification, the output of the transmission arm experiences nonlinear pulse evolution and its pulse width is directly compressed to 123 fs (almost approaches the calculated Fourier transform limited duration of 114 fs), along with the scaling of the average power to 80 mW. Moreover, through characterizing the noise properties of the laser, it is found that the phase noise, intensity noise and the signal-to-noise ratio (SNR) of the fundamental repetition frequency at the transmission arm manifests a better performance than at the reflection arm. With an integration frequency of [3 kHz, 1 MHz], an optimal timing jitter and relative intensity noise of 164 fs and 0.006% are, respectively, obtained. The noise suppression mechanism is attributed to the interaction between the transmission curve of the NALM and the pulse peak power fluctuations, as well as the dispersion management of the cavity. In addition, the stable operation of the laser is further verified by monitoring the long-term stability.

Stable femtosecond pulse generation relying on a simple NALM-based all PM Tm-doped fiber laser

Herein, an ultrafast mode-locked Tm-doped fiber laser with all polarization-maintaining (PM) fiber relying on nonlinear amplifying loop mirror was firstly presented. The simple all-PM mode-locked oscillator can deliver output power of ∼1.20 mW and pulse repetition of ∼7.267 MHz at central wavelength of ∼1950.2 nm. The pulse duration was measured after boosting the power to ∼20 mW by a fiber amplifier, which shows the full width at half maximum (FWHM) of ∼357 fs. Moreover, the all-PM mode-locked oscillator has exhibited a good power stability with fluctuation of ∼1.08 % during 36 h monitoring. This stable fiber laser might be served as a potential ultrashort pulse seed source for the applications of medical treatment, precision processing and mid-infrared light source.

Mode-locked Tm-doped fiber laser induced by ferroferric-oxide nanoparticles and a D-shaped fiber

• We demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). This is the first use of FONPs to achieve mode-locking at 2um. • The mode-locking operates in 1931 nm, the 3 dB bandwidth is 5.9 nm, the repetition frequency is 24 MHz, and the pulse width is 1.29 ps. In addition, the signal-to-noise ratio is ∼67 dB, indicating the stability of the output spectrum. As a unique type of transition metal oxides, ferroferric-oxide nanoparticles (FONPs) have attracted much attention due to their outstanding physical and chemical properties. In this paper, we demonstrate a passively mode-locked laser operating at 2 um region based on a saturable absorber (SA) of FONPs deposited on the D-shaped fiber (DF). FONPs were deposited on DF to form FONP-DF SA devices. As inserted into the thulium-doped fiber laser (TDFL), a mode-locked pulse was realized at 1931 nm. For all we know, this is the first demonstration of FONP-DF SA in fiber lasers at 2 um region. This work fills the gap of FNOP in the realization of 2 um mode-locking and lays the foundation for us to use FNOP-DF for magnetic field sensing in the future.

Ultrafast Tm-doped fiber laser based on hybrid fiber coupler

Tm-doped ultrafast fiber lasers have been widely used in scientific research and industrial applications. Here, with the usage of an novel integrated fiber coupler, we describe a reduced laser configuration to achieve compact and high-performance all-fiber Tm-doped mode-locked fiber laser. This novel fiber component can be used as wavelength division multiplexer (WDM), output coupler (OC) and optical modulator at the same time, fabricated by magnetron-sputtering vanadium dioxide (VO2) saturable absorber (SA) on a optical coupler. The bare coupler was laboratory-tapered performing WDM and OC simultaneously. With above-mentioned device, a mode-locked Tm-doped fiber laser was constructed. Fundamental solitons were formed and generated with a short pulse width of 478 fs and a high repetition rate of 160 MHz. In addition, Short-term and long-term laser stability was confirmed by the noise analysis and 4-h running test. 336 fs RMS time jitter ([10 kHz - 10 MHz]) and 0.036% RMS relative intensity noise ([1 Hz - 10 MHz]) was acquired. This new integrated design at 2 μm region simplifies implementation of the ultrafast Tm-doped fiber laser and paves the way for developing compact and high-performance all-fiber ring laser.

214 MHz, 450 fs mode-locked Tm-doped fiber laser with a WTe2&gain fiber integrated fiber coupler

We report a WDM/OC/SA/TDF multifunctional integrated tapered coupler for the first time. By magnetron sputtering WTe2 on the conical region of the coupler, it can be served as a wavelength division multiplexer (WDM), output coupler (OC), saturable absorber (SA), and gain medium. The thulium-doped mode-locked fiber laser based on such integrated device was centered at 1966.6 nm with 450 fs duration and a fundamental repetition frequency of 214 MHz. The long-term operating stability and the noise feature of mode-locked laser was also characterized. At the same time, the 10th harmonic mode-lockeing (HML) at the repetition rate of 2.14 GHz was demonstrated in the cavity, to the best of our knowledge, which was the highest repetition rate reported for SA-based mode-locked fiber lasers in 2 µm region.

1.7 µm figure-9 Tm-doped ultrafast fiber laser.

The evolution of multiphoton microscopy is critically dependent on the development of ultrafast laser technologies. The ultrashort pulse laser source at 1.7 µm waveband is attractive for in-depth three-photon imaging owing to the reduced scattering and absorption effects in biological tissues. Herein, we report on a 1.7 µm passively mode-locked figure-9 Tm-doped fiber laser. The nonreciprocal phase shifter that consists of two quarter-wave plates and a Faraday rotator introduces phase bias between the counter-propagating beams in the nonlinear amplifying loop mirror. The cavity dispersion is compensated to be slightly positive, enabling the proposed 1.7 µm ultrafast fiber laser to deliver the dissipative soliton with a 3-dB bandwidth of 20 nm. Moreover, the mode-locked spectral bandwidth could be flexibly tuned with different phase biases by rotating the wave plates. The demonstration of figure-9 Tm-doped ultrafast fiber laser would pave the way to develop the robust 1.7 µm ultrashort pulse laser sources, which could find important application for three-photon deep-tissue imaging.

Tunable mode-locked Tm-doped fiber laser based upon cross-phase modulation.

We demonstrate the generation of soliton and dissipative soliton in an ultrafast thulium (Tm) doped fiber laser based upon cross-phase modulation (XPM) induced mode-locking. The mode-locking is realized by periodically modulating the 2-µm signal through XPM that is activated by an injected 1.5-µm pulsed laser. Such a mechanism enables the laser to be mode-locked in various operation regimes without any real or artificial saturable absorbers. Thanks to the XPM pulling effect, the wavelength of the Tm-doped fiber laser can be tuned by adjusting the repetition frequency of the 1.5-µm pulsed laser. The maximum tuning ranges achieved in this work for the soliton and dissipative soliton regimes are respectively 11 nm and 15 nm. The outcomes of this work not only provide a continuously and controllably wavelength-tunable ultrafast laser but also offer a passively synchronized dual-color fiber laser system, which is promised for many important applications such as Raman spectroscopy, nonlinear frequency conversion systems, and multi-color pump-probe systems.

All-Fiber Mid-Infrared Supercontinuum Generation Pumped by Ultra-Low Repetition Rate Noise-Like Pulse Mode-Locked Fiber Laser

We demonstrate broadband mid-infrared supercontinuum generation in a piece of indium fluoride fiber pumped by an ultralow repetition rate noise-like pulse mode-locked fiber laser. This figure-9 mode-locked Tm-doped fiber laser has a long laser cavity by inserting a piece of standard single mode fiber and a piece of dispersion compensation fiber, which delivers mode-locked noise-like pulse with a repetition rate of ∼190 kHz. The mode-locked noise-like pulse train has a low pulse duty cycle of 4.38 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . With only one Tm-doped fiber amplifier, the ultra-low repetition rate noise-like pulse is amplified to ∼3 W. The pulse energy is boosted to ∼15 μJ with a peak power of ∼6.5 kW. Pumping a piece of highly nonlinear indium fluoride fiber with the amplified noise-like pulse, a flat mid-infrared supercontinuum with a covering range from ∼1500 nm to ∼4100 nm can be achieved. Due to the low operational power, no cooling installations are required to control the temperature of the supercontinuum laser system. This all-fiber mid-infrared SC laser source has a relatively simple architecture and low cost. This study demonstrates the great advantages of this type of ultra-low repetition rate noise-like pulses in mid-infrared supercontinuum generation.

Novel two-dimensional semi-metallic NiTe2 based saturable absorber for ultrafast mode-locked fiber laser

Two-dimensional transition metal dichalcogenides (TMDs) have been widely used in ultrafast optics. However, the traditional TMDs such as MoS2 and WS2 have narrow operating band and slow carrier recovery time, limiting their practical application. Among various kinds of TMDs, nickel ditelluride (NiTe2) is a special type-II Dirac semi-metallic TMD material developed recently, showing great potential in ultrafast pulse generation due to its broadband optical response, ultrafast carrier recovery time, strong light-matter interaction and high chemical stability. Nevertheless, there has been no research reported on the NiTe2 based saturable absorber (SA) and its application in the mode-locked laser at the 1.5 and 2 μm regions. In this work, few-layer NiTe2 nanosheets were prepared and SA device was further fabricated by depositing them on a tapered fiber. The saturable absorption property of NiTe2 SA was confirmed by using a balanced twin-detector measurement system. With the use of NiTe2 SA, the Er-doped mode-locked fiber laser with a central wavelength of 1567.3 nm and a pulse width of 1.07 ps was achieved. Moreover, the Tm-doped mode-locked fiber laser with a central wavelength of 1966.08 nm was also obtained based on the NiTe2 SA. These results show that NiTe2 is a promising SA material for ultrafast pulse laser.

950 nm Femtosecond Laser by Directly Frequency-Doubling of a Thulium-Doped Fiber Laser

We demonstrate a compact and efficient femtosecond laser operating at ~950 nm by directly frequency-doubling of a mode-locked Tm-doped fiber laser. The laser is based on a highly compact architecture, with a dispersion-managed oscillator together with only one-step frequency conversion. The output pulse width is ~270 fs, with a repetition rate of 22.1 MHz and a pulse energy of 12.9 nJ. It is believed that the greatly simplified setup makes the current laser well suited for two-photon microscopy and other biomedical and clinical applications.

>10 GHz femtosecond fiber laser system at 2.0 μm.

We demonstrate a high-power 2.0-μm fiber laser system delivering femtosecond pulses with a fundamental repetition rate of >10 GHz, the highest value so far, to the best of our knowledge. The seed is a self-started fundamentally mode-locked Tm-doped fiber laser that has excellent power and spectral stabilities. The laser system can provide an average power of >600 mW, and the use of soliton-effect-based pulse compression allows the achievement of a pulse duration of 163 fs, leading to a compression factor of ∼ 13. It is anticipated that this new high-power femtosecond fiber laser with a 10-GHz-level fundamental repetition rate can serve as a promising light source for various applications, including laser surgery, micromachining, frequency comb spectroscopy, and nonlinear frequency conversion.

Real-time observation of chaotic and periodic explosions in a mode-locked Tm-doped fiber laser.

We experimentally characterize the dynamics of soliton explosions in a transient chaotic state between a single and double pulsing state, as well as periodic explosions induced by soliton collisions in a dual wavelength soliton state. These explosions occurring in a thulium-doped linear fiber laser with net anomalous dispersion are characterized with real-time measurements based on a modified time-stretched dispersive Fourier transform method relying on second-harmonic generation.

Mode-Locked Tm-Doped Fiber Laser Induced by Ferroferric-Oxide Nanoparticles and a D-Shaped Fiber

Mode-Locked Tm-Doped Fiber Laser Induced by Ferroferric-Oxide Nanoparticles and a D-Shaped Fiber

Research on a 1.7 μm all-fiber mode-locked Tm-doped fiber laser

Research on a 1.7 μm all-fiber mode-locked Tm-doped fiber laser

Adaptive genetic algorithm-based 2 μm intelligent mode-locked fiber laser

The emission wavelength of an ultrafast laser generated by thulium (Tm)-doped fiber laser (TDFL) ranges from 1.7 to 2.1 μm, covering the water-absorbing band and atmospheric transmission window. In this study, an intelligent Tm-doped mode-locked fiber laser was experimentally demonstrated by combining a genetic algorithm (GA) with an adaptive mutation rate and a nonlinear polarization rotation mode-locked fiber oscillator. A closed-loop feedback system was set up in the experiment, including an oscilloscope, a laptop computer, an electric polarization controller, and a mode-locked fiber oscillator. Based on the aforementioned intelligent design of manual-operation-free, a stable femtosecond level noise-like-mode-locked pulse with an output power of 57.7 mW and a central wavelength of 1973 nm was automatically generated. The evolutionary dynamics of the different parameter structures of the GA-controlled ultrafast TDFL with varying mutation rates were also investigated. This study will pave the way for generating robust ultrafast lasers in the short-wave infrared region.

Generation of few-cycle pulses from a mode-locked Tm-doped fiber laser

We report a compact, self-starting dispersion-managed mode-locked thulium-doped fiber oscillator that delivers 2.6 nJ pulses at 2 µm with a repetition rate of 250 MHz. The average output power and spectral bandwidth of the pulses reach impressive values of 648 mW and 103 nm, respectively. The generated pulses are near linearly chirped, capable of linearly compressing to 74 fs in a normal dispersion fiber after power attenuation. Using a nonlinear fiber compression scheme can even compress the pulses to 29 fs (4.3-cycle). The remaining pulse energy is 1.15 nJ, and the corresponding peak power is estimated as 39.4 kW. To the best of our knowledge, this is the first demonstration of nonlinearly compressing the pulse of a 2 µm fiber oscillator to the sub-5 cycle regime. Such a few-cycle fiber laser could be an ideal candidate source for short-wavelength mid-infrared frequency metrology and molecular spectroscopy applications.

Mid-infrared supercontinuum generation of 1.14 W in a fluoroindate fiber pumped by a fast gain-switched and mode-locked thulium-doped fiber laser system

We report the generation of a spectrally flat supercontinuum in a fluoroindate ( I n F 3 ) fiber with a maximum time-averaged output power of 1.14 W and a spectrum extended to 4.75 µm. The pump source was a fast gain-switched and semiconductor saturable absorber mirror mode-locked thulium Tm-doped fiber laser followed by a cascade of two Tm-doped fiber amplifiers. The repetition rates of the gain-switched pulses and mode-locked sub-pulses were 50 kHz and 111 MHz, respectively, whereas the duration of sub-pulses recorded within a gain-switched pulse envelope was ∼ 110 p s . This home-built pump laser system provided an output average power of 2.45 W at a central wavelength of 2 µm. To the best of our knowledge, this is the first paper on supercontinuum generation in an I n F 3 fiber pumped by a fast gain-switched and mode-locked laser system. This approach is promising for further efficient continuum generation in the mid-infrared region.