Comprehensive analysis of pure-quartic soliton dynamics in a passively mode-locked fiber laser

The understanding of soliton dynamics promotes the development of ultrafast laser technology. High-energy purequartic solitons(PQSs) have gradually become a hotspot in recent years. Herein, we numerically study the influence of the gain bandwidth, saturation power, small-signal gain, and output coupler on PQS dynamics in passively mode-locked fiber lasers. The results show that the above four parameters can affect PQS dynamics. Pulsating PQSs occur as we alter the other three parameters when the gain bandwidth is 50 nm. Meanwhile, PQSs evolve from pulsating to erupting and then to splitting as the other three parameters are altered when the gain bandwidth is 10 nm, which can be attributed to the existence of the spectral filtering effect and intra-cavity fourth-order dispersion. These findings provide new insights into PQS dynamics in passively mode-locked fiber lasers.

Interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.

Single output LD end-pumped passively mode-locked Nd:YVO_4 laser with semiconductor saturable absorber mirror

A quarter-wave plate and the thin film polarizer （TFP） are used for the LD end-pumped passively mode-locked Nd：YVO4 laser with semiconductor saturable absorber mirror （SESAM） to obtain a single beam output with a total power of 4.8 W. An optical-optical efficiency is achieved to be 24% for a stable CW mode-locking operation at 1064 nm, with a pulse repetition rate of 70 MHz and pulse width of 16 ps. The multipulse in the pulse sequence is eliminated for reaching a peak power as high as 4 kW.

Reflective graphene oxide absorber for passively mode-locked laser operating at nearly 1μm

A low cost and simply fabricated reflective graphene oxide is successfully made. By using this absorber, as well as an end reflector, we obtain a passively mode-locked Yb：LuYSiO5 laser operating at nearly 1 p,m. When the pump power is increased up to 5.73 W, stable mode locking is achieved. The central wavelength of the laser spectrum is 1043.2 nm with a pulse duration of 5.0 ps. When the pump power reaches 8.16 W, dual-wavelength mode locking laser pulses at 1036.3 nm and 1043.5 nm are simultaneously detected.

Passively Mode-Locked Femtosecond Disordered Crystal Laser with Nd:CGA as Gain Medium

We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd：CaGdAI04 （Nd：CGA） as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd：CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.

Diode-Pumped Passively Mode-Locked 1079 nm Nd:CaGdAlO_4 Laser

We demonstrate a diode-pumped passively cw mode-locked Nd：CaGdAlO4 laser operating at 1079nm with a semiconductor saturable absorber mirror for the first time to the best of our knowledge. The threshold pump power of the laser is 180mW. A maximum average output power of 93mW is obtained under the pump power of 1.94 W. The pulse duration of the mode-locked pulses is 3.1ps and the repetition rate is 157MHz.

Chirp Extraction of Self-Similar Pulses in a Passively Mode-Locked Er-doped Fiber Laser

In this paper, we adopt cloud computing in a specific scientific computing field for its virtualization, distribution and dynamic extendibility as follows: We obtain high-energy parabolic self-similar pulses by numerical simulation using our non-distributed passively mode-locked Er-doped fiber laser model. For researching characteristics of these wave-breaking-free self-similar pulses, chirp of them must be extracted. We propose several time-frequency analysis methods adopted in chirp extraction of ultra-short optical pulses for the first time and discuss the advantages and disadvantages of them in this particular application.

Raman-Assisted Passively Mode-Locked Fiber Laser

We propose and demonstrate a Raman-assisted passively mode-locked Yb-doped fiber laser in a normal dispersion regime. A section of highly nonlinear fiber is adopted to enhance the nonlinearity to extend the bandwidth of the gain spectrum by the stimulated Raman effect. The mode-locked fiber laser emits a broad spectral bandwidth of 64 nm at the-20 dB level and a highly stable pulse operation with a signal-to-noise ratio of 77 dB.

Passively mode-locked 2-μm Tm:YAP laser with a double-wall carbon nanotube absorber

We report on a diode-pumped passively continuous wave （cw） mode-locked Tm：YAP laser with a double-wall carbon nanotube （DWCNT） absorber operating at a wavelength of 2023 nm for the first time, to the best our knowledge. The DWCNT absorber is fabricated on a hydrophilic quartz substrate by using the vertical evaporation technique. The output power is as high as 375 mW. A stable pulse train with a repetition rate of 72.26 MHz is generated with a highest single pulse energy of 5.2 μJ.

Generation and evolution of multiple operation states in passively mode-locked thulium-doped fiber laser by using a graphene-covered-microfiber

Using graphene-covered-microfiber （GCM） as a saturable absorber, the generation and evolution of multiple operation states are proposed and demonstrated in passively mode-locked thulium-doped fiber laser. The microfiber was fabricated using the flame brushing method to an interaction length of - 1.2 cm with a waist diameter of -10 μm. Graphene layers were grown on copper foils by chemical vapor deposition and transferred onto the polydimethylsiloxane （PDMS） to form a PDMS/graphene film, which allowed light-graphene interaction via evanescent field. With the increase of the pump power from 1.25 W to 2.15 W, five different lasing regimes, including continuous-wave, conventional soliton mode-locking, multi- soliton mode-locking, a period of transition, and noise-like mode-locking, were achieved in a fiber ring cavity. To the best of our knowledge, it is the first report of the generation and evolution of multiple operation states by covering graphene on the microfiber in the 2-μ.m region. The results demonstrate that GCM can be a promising method for fabricating all fiber SA, and the switchable operation states can provide more portability in complex application domain.

High power diode-pumped passively mode-locked Nd:YVO_4 laser at repetition rate of 3.2 GHz

A compact high power diode-pumped passively mode-locked Nd:YVO_4 laser with high repetition rate is realized.Using an Nd:YVO_4 crystal and a semiconductor saturable absorber mirror(SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square(RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours,showing a superior stability with the compact configuration.

Impacts of operational parameters on nonlinear polarization rotation-based passively mode-locked fiber laser

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper.The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shro¨dinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser.The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power.The periodicity of the polarization controlling is observed.With given pump power,there exists a set of polarization controlling under which the ultra-short pulse can be generated.With given polarization controlling,the mode-locked state can be maintained generally except for some particular values of pump power.Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes.The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.

Reduced graphene oxide as saturable absorbers for erbium-doped passively mode-locked fiber laser

We demonstrate a nanosecond mode-locked erbium-doped fiber laser （EDFL） based on a reduced graphene oxide （RGO） saturable absorber （SA）. The RGO SA is prepared by depositing the graphene oxide （GO） on fluorine mica through thermal reduction of GO. A scanning electron microscope （SEM）, Raman spectrometer, and x-ray photoelectron spec- troscopy （XPS） are adopted to analyze the RGO characteristics. The results show that the reduction degree of graphene oxide is very high. By embedding the RGO SA into the EDFL cavity, a stable mode-locked fiber laser is achieved with a central wavelength of 1567.29 nm and repetition rate of 12.66 MHz. The maximum output power and the minimum pulse duration are measured to be 18.22 mW and 1.38 ns respectively. As far as we know, the maximum output power of 18.22 mW is higher than those of other nanosecond mode-locked oscillators reported. Such a nanosecond pulse duration and megahertz repetition rate make this mode-locked erbium-doped fiber laser a suitable seed oscillator for high-power applications and chirped pulse amplifications.

Bound soliton pulses in a passively mode-locked fibre ring laser

The bound solitons in a passively mode-locked fibre ring laser are observed and their formation mechanism is summarized in this paper. In order to obtain stable bound solitons, a strong CW laser field at the centre of the soliton spectral is necessary to suppress and synchronize the random soliton phase variations.

575-fs passively mode-locked Yb:CaF2 ceramic laser

A Yb-doped CaF2 transparent ceramics was successfully fabricated by the hot-pressed method and its laser characteristics were studied.A broad tuning performance and mode-locked laser operation were demonstrated in this ceramics for the first time,to our best knowledge.A 60-nm continuous-wavelength tunable laser from 1019 nm to 1079 nm was obtained with a birefringent filter.By employing a semiconductor saturable absorber mirror without additional dispersion compensation elements,a continuous-wave mode-locked laser with pulse duration as short as 575 fs was delivered,at a central wavelength of 1048.5 nm.The oscillator is operated under a repetition rate of 55 MHz.These results indicate that the Yb:CaF2 transparent ceramics is an ideal candidate for the development of ultrafast lasers in the near-infrared regime.

Wavelength-tunable prism-coupled external cavity passively mode-locked quantum-dot laser

A wavelength-tunable mode-locked quantum dot laser using an InAs/GaAs quantum-dot gain medium and a discrete semiconductor saturable absorber mirror is demonstrated. A dispersion prism, which has lower optical loss and less spectral narrowing than a blazed grating, is used for wavelength selection and tuning. A wavelength tuning range of 45.5 nm （from 1137.3 nm to 1182.8 nm） under 140-mA injection current in the passive mode-locked regime is achieved. The maximum average power of 19 mW is obtained at the 1170.3-nm wavelength, corresponding to the single pulse energy of 36.5 pJ.

Zinc-oxide/PDMS-clad tapered fiber saturable absorber for passively mode-locked erbium-doped fiber laser

We propose and demonstrate a passively mode-locked erbium-doped fiber laser(EDFL)based on zinc-oxide/polydimethylsiloxane(ZnO/PDMS)saturable absorber(SA)that evanescently interacts with the light on a tapered fiber.The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device,with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%.The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW.The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps,respectively.These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient,compatible,and low-cost SA device for ultrafast laser applications.

Observation of stable bound soliton with dual-wavelength in a passively mode-locked Er-doped fiber laser

A phase-locked bound state soliton with dual-wavelength is observed experimentally in a passively mode-locked Erdoped fiber（EDF） laser with a fiber loop mirror（FLM）. The pulse duration of the soliton is 15 ps and the peak-to-peak separation is 125 ps. The repetition rate of the pulse sequence is 3.47 MHz. The output power is 11.8 mW at the pump power of 128 mW, corresponding to the pulse energy of 1.52 nJ. The FLM with a polarization controller can produce a comb spectrum, which acts as a filter. By adjusting the polarization controller or varying the pump power, the central wavelength of the comb spectrum can be tuned. When it combines with the reflective spectrum of the fiber Bragg grating, the total spectrum of the cavity can be cleaved into two parts, then the bound state soliton with dual-wavelength at 1549.7 nm and 1550.4 nm is obtained.

Yb-doped passively mode-locked fiber laser with Bi_2Te_3-deposited

In this study we present an all-normal-dispersion Yb-doped fiber laser passively mode-locked with topological insulator（Bi2Te3） saturable absorber. The saturable absorber device is fabricated by depositing Bi2Te3 on a tapered fiber through using pulsed laser deposition（PLD） technology, which can give rise to less non-saturable losses than most of the solution processing methods. Owing to the long interaction length, Bi2Te3 is not exposed to high optical power, which allows the saturable absorber device to work in a high power regime. The modulation depth of this kind of saturable absorber is measured to be 10%. By combining the saturable absorber device with Yb-doped fiber laser, a mode-locked pulse operating at a repetition rate of 19.8 MHz is achieved. The 3-d B spectral width and pulse duration are measured to be 1.245 nm and317 ps, respectively.

Ultrashort Pulse Generation at Quasi-40-GHz by Using a Two-Section Passively Mode-Locked InGaAsP-InP Tensile Strained Quantum-Well Laser

A 1.56 μm passively mode-locked laser diode with a two-section tensile strained multi-quantum-well structure is fabricated.Without any external pulse compression,a Lorentz pulse train with a pulse width of 1.03 ps and a repetition rate of 35.6 GHz is obtained,which is one of the best results that have been reported on similar devices.The optical pulse has a 300 kHz line width and a 50dB peak over the noise floor in the photodetected radio-frequency electrical spectrum.