MoS_2 saturable absorber prepared by chemical vapor deposition method for nonlinear control in Q-switching fiber laser

Due to the remarkable carrier mobility and nonlinear characteristic, MoS2 is considered to be a powerful competitor as an effective optical modulated material in fiber lasers. In this paper, the MoS2 films are prepared by the chemical vapor deposition method to guarantee the high quality of the crystal lattice and uniform thickness. The transfer of the films to microfiber and the operation of gold plated films ensure there is no heat-resistant damage and anti-oxidation. The modulation depth of the prepared integrated microfiber-MoS2 saturable absorber is 11.07%. When the microfiber-MoS2 saturable absorber is used as a light modulator in the Q-switching fiber laser, the stable pulse train with a pulse duration of 888 ns at 1530.9 nm is obtained. The ultimate output power and pulse energy of output pulses are 18.8 mW and 88 nJ, respectively. The signal-to-noise ratio up to 60 dB indicates the good stability of the laser. This work demonstrates that the MoS2 saturable absorber prepared by the chemical vapor deposition method can serve as an effective nonlinear control device for the Q-switching fiber laser.

Switching,explosion,and chaos of multi-wavelength soliton states in ultrafast fiber lasers

Because of the complexity and difficulty of realizing a multi-wavelength soliton state,reports on its internal dynamic characteristics are scarce.In this study,the switching and periodic soliton explosion processes of the multi-wavelength soliton state in a negative dispersion passively mode-locked fiber laser are realized.The generation of the multi-wavelength soliton state undergoes the process of noise,oscillation,and stable mode-locking,and the splitting and annihilation of solitons with different group velocities directly impact the generation and disappearance of three wavelengths.Positive and negative dispersion lead to different group velocities of solitons.The presence and displacement of solitons with different group velocities cause soliton collisions,which lead to soliton explosions.A soliton experiences relative phase oscillation,chaos,and oscillation,as well as convergence and separation before and after an explosion.With an increase in parameters related to pump power,single-soliton oscillation,multi-wavelength solitons,and chaos are found in experiments and simulations,proving the relevance and reliability between simulation and experimental results.This work promotes the dynamical study of multi-soliton collisions in nonlinear science and the development of chaos theory in multi-comb lasers.

A theoretical and experimental investigation of an in-band pumped gain-switched thulium-doped fiber laser

In this paper, the theoretical rate equation model of an in-band pumped gain-switched thulium-doped fiber （TDF） laser is investigated. The analytical formulations of pump energy threshold, peak power extraction efficiency, and pulse extraction efficiency are derived through analyzing the interaction process between the pump pulse and the laser pulse. They are useful for understanding, designing, and optimizing the in-band pumped TDF lasers in a 1.9 μm-2.1 μm wavelength region. The experiment with an all-fiber gain-switched TDF laser pumped by a 1.558-μm pulse amplifier is conducted, and our experimental results show good agreement with theoretical analysis.

A compact graphene Q-switched erbium-doped fiber laser using optical circulator and tunable fiber Bragg grating

We demonstrate a passively Q-switched tunable erbium-doped fiber laser （EDFL） based on graphene as a saturable absorber （SA）. A three-port optical circulator （OC） and a strain-induced tunable fiber Bragg grating （TFBG） are used as the two end mirrors in an all-fiber linear cavity. The Q-switched EDFL has a low pump threshold of 23.8 mW. The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from 23.8 mW to 219.9 mW. The minimum pulse duration is 1.7 p.s and the highest pulse energy is 25.4 nJ. The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.

High-energy pulse generation using Yb-doped Q-switched fiber laser based on single-walled carbon nanotubes

An all-fiber laser using a single-walled carbon nanotube（SWCNT） as the saturable absorber（SA） for Q-switched operation in the 1031 nm region is demonstrated in this work. A lasing threshold as low as 17 mW was realized for continuous wave operation. By further increasing the pump power, stable Q-switched pulse trains are obtained when the pump power ranges from 38 mW to 125 mW, corresponding to repetition rate varying from 40.84 kHz to 66.24 kHz, the pulse width from 2.0 μs to 1.0 μs,and the highest single pulse energy of 40.6 nJ respectively.

Recent Progresses on Passively Switched Mid-Infrared Fiber Lasers at 3 μm

We present the recent research progress of our group on mid-infrared pulsed fiber lasers at 3μm by passive switching. Three different kinds of saturable absorbers including semiconductor saturable absorber （SESAM）, Fe2＋：ZnSe crystal, topological insulator （TI） were used to perform the pulse generation, respectively. The temporal regimes of mode locking, Q-switching and Q-switching induced gain switching were gained. Some relative discussions and prospective efforts are proposed at the end of this paper.

Analysis of New Q-switched Erbium Doped Fiber Laser Based on Fiber Grating Loop Mirror

An all fiber wavelength selective Q switching modulator based on fiber grating loop mirror is proposed. A newly configured Q switched erbium doped fiber laser using this all fiber modulator is numerically analyzed taking into account the effects of the spontaneous emission.

Tandem-pumped 1120-nm actively Q-switched fiber laser

We report on a tandem-pumped actively Q-switched fiber laser system emitting at 1120 nm.Parasitic oscillation is challenging in Yb-doped Q-switched 1120-nm fiber laser,which is suppressed by pumping with a fiber laser at 1018 nm.At least four times improvement in output peak power is demonstrated in a single laser setup with 1018-nm fiber laser pumping instead of 976-nm laser diode pumping.This is,to the best of our knowledge,the first demonstration of a tandem-pumped Q-switched fiber laser.

High conversion efficiency, high power density Q-switched fiber laser

An acoustic-optic Q-switched all-fiber laser With a high-repetition-rate, a short pulse width, a wide spectrum, and a high conversion efficiency is experimentally demonstrated. In the laser configuration, a （1＋1）x 1 side-pumping coupler is introduced to perform backward pumping, and a 10/130%tm Yb fiber is adopted. The acoustic-optic component operates in the first direction, achieving a Q-switched pulse with a repetition rate adjustable in the range of 20 kHz-80 kHz. Under a repetition rate of 20 kHz and a pump power of 6.76 W, the fiber laser obtains a highly efficient and stable pulse output, with an average power of 4.3 W, a pulse width of 56 ns, a peak power of 3.83 kW, and a power density of 1.39x 101~ W/cm2. Particularly, the optic-optic conversion efficiency of the laser reaches as high as 64%. Another feature of the pulsed laser is that the high reflection mirror reflects the pump light as well, which brings the secondary absorption of the pump power into the gain fiber.

Passively Q-Switched Erbium-Doped Fiber Laser Based on GeSe Saturable Absorber

GeSe nanosheets were prepared by ultrasonic-assisted liquid phase exfoliation (LPE), and the nonlinear saturated absorption performance was experimentally studied. The modulation depth and saturation intensity of the prepared GeSe saturable absorber (SA) were 15% and 1.44 MW/cm2, respectively. Using the saturated absorption characteristics of GeSe SA, a passively Q-switched erbium-doped fiber laser was systematically demonstrated. As the pump power increases, the pulse repetition frequency increases from 22.8 kHz to 77.59 kHz. The shortest pulse duration is 1.51 μs, and the corresponding pulse energy is 46.14 nJ. Experimental results show that GeSe nanosheets can be used as high-efficiency SA in fiber lasers. Our results will provide a useful reference for demonstrating pulsed fiber lasers based on GeSe equipment.

Passively Q-Switched Erbium-Doped Fiber Laser with TiSe₂as Saturable Absorber

The TiSe2 nanosheets were prepared by means of ultrasound-assisted liquid phase exfoliation (LPE) and the nonlinear saturable absorption properties were experimentally investigated. The modulation depth, saturation intensity and nonsaturable absorbance of the prepared 1T-TiSe2 SA were 15.7%, 1.28 MW/cm2 and 8.2%, respectively. Taking advantage of the saturable absorption properties of TiSe2-based SA, a passively Q-switched erbium-doped fiber (EDF) laser was systematically demonstrated. The pulse repetition rates varied from 24.50 kHz up to 73.79 kHz with the increasing pump power. The obtained shortest pulse width was 1.31 μs with pulse energy of 79.28 nJ. The system presented merits of low-cost SA preparation, system compactness, superb stability and high competition.

Pulse generation of erbium-doped fiber laser based on liquid-exfoliated FePS3

As a preferable material in the field of photo-detection and catalysis,the characteristics of FePS3 in broad wavelength range have been proven by many experimental studies.However,FePS3 has not been used as a saturable absorber(SA)in fiber lasers yet.We propose and demonstrate the generation of a single wavelength and dual-wavelength based on an Er-doped fiber laser(EDFL)at 1.5μm by using an innovative FePS3 saturable absorber for the first time.The result shows that a stable passively Q-switched pulse can be generated,which demonstrates that the new two-dimensional(2D)material FePS3 served as SA provides a valid method to realize passively Q-switched laser.In addition,we achieve the output of the dual-wavelength pulse by properly rotating the polarization controller.To the best of our knowledge,the dual-wavelength pulse EDFL could be applied in biomedicine,spectroscopy,and sensing research.

Zinc-oxide nanoparticle-based saturable absorber deposited by simple evaporation technique for Q-switched fiber laser

A Q-switched erbium-doped fiber laser(EDFL)incorporating zinc-oxide(ZnO)nanoparticles-based saturable absorber(SA)is proposed and demonstrated.To form the SA,the ZnO nanoparticles,which are originally in the powder form,are first dissolved in ethanol and subsequently deposited onto the surface of fiber ferrule by using the adhesion effect with the evaporation technique.By integrating the ZnO nanoparticle-based SA into a laser cavity of an EDFL,a self-started and stable Q-switching is achieved at a low threshold power of 20.24 mW.As the pump power is increased,the pulse repetition rate is tunable from 10.34 kHz to 25.59 kHz while pulse duration decreases from 21.39μs to 3.65μs.Additionally,this Q-switched laser has a maximum energy per pulse of 19.34 nJ and an average output power of 0.46 mW.These results indicate the feasibility and functionality of the ZnO nanoparticles-based SA for Q-switched generation,which offers the flexibility and easy integration of the SA into a ring laser cavity.

Experimental investigation on Q-switching and Q-switched mode-locking operation in gold nanorods-based erbium-doped fiber laser

We report on the generation of Q-switched and Q-switched mode-locked （QML） pulses in an erbium-doped fiber ring laser by using a polyvinyl alcohol （PVA） -based gold nanorod （GNR） saturable absorber （SA）. The PVA- based GNR SA has a modulation depth of -4.8% and a non-saturable loss of -26.9% at 1.5 μm. A Q-switched pulse train with a repetition rate varying from 18.70 to 39.85 kHz and a QML pulse train with an envelope repetition rate tuning from 20.31 to 31.50 kHz are obtained. Moreover, the lasing wavelengths of the Q-switched pulses can be flexibly tuned by introducing a narrow bandwidth, tunable filter into the laser cavity. The results demonstrate that the GNRs exhibit good optical performance and can find a wide range of applications in the field of laser technology.

Laser-driven self-exfoliation of graphene oxide layers on a fiber facet for Q switching of an Er-doped fiber laser at the longest wavelength

A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide(GO)selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation.Using the GO colloid droplet with sub-nanoliter volume,we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc.The prepared fiber facet was then included in an Er-doped fiber laser(EDFL)cavity and we obtained a few layers of GO having nonlinear optic two-dimensional(2D)characteristics selectively on the fiber core by the laser-driven self-exfoliation.The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation atλ
1600.5 nm,the longest Q-switched laser wavelength in EDFLs.Pulse characteristics were analyzed as we varied the pump power atλ
980 nm from 105.2 mW to 193.6 mW,to obtain the maximum repetition rate of 17.8 kHz and the maximum output power of 2.3 mW with the minimum pulse duration of 7.8μs.The proposed method could be further applied to other novel inorganic 2D materials opening a window to explore their novel nonlinear optic laser applications.

Dual-wavelength stable nanosecond pulses generation from cladding-pumped fiber laser

In this paper, the generation of dual-wavelength stable nanosecond pulses by a laser diode pumped Yb doped double-clad fiber laser is presented. In the experiment, the fiber laser with two-mirror cavity is approved which operates in a self-Q-switching regime. The Q-switching mechanism is based on stimulated Brillouin scattering （SBS）. When the pump power achieves the SBS threshold, the fiber laser changes from the start resonator to the SBS resonator. With different reflectivities of the second mirror, stable dual-wavelength pulses with the pulse width range from 10 ns to less than 2 ns are obtained. The result was explained theoretically by birefringency （including stochastic birefringency and bend birefringency）. OCIS codes： 140.3510, 290.5900, 320.4240, 260.1440.

Actively Q-switched ring Tm-doped fiber laser with free space structure

We report a cladding-pumped actively Q-switched ring Tm-doped fiber laser（TDFL）. This laser is Q-switched by a free space acousto-optic modulator. A pulse energy up to 150 μJ with a pulse width of 207 ns at a repetition rate of100 Hz is achieved for a cavity optical length of 6.68 m. The pulse amplitude’s stability at this repetition rate is better than 95%. To the best of our knowledge, this is the first free space structure Q-switched ring TDFL report.

High-energy all-fiber gain-switched thulium-doped fiber laser for volumetric photoacoustic imaging of lipids

We demonstrate a high-energy all-fiber short wavelength gain-switched thulium-doped fiber laser for volumetric photoacoustic(PA)imaging of lipids.The laser cavity is constructed by embedding a short piece of gain fiber between a pair of fiber Bragg gratings(FBGs).Through using three pairs of FBGs with operation wavelengths at1700,1725,and 1750 nm,three similar lasers are realized with a cavity length of around 25 cm.Under a maximum pump energy of 300μJ at 1560 nm,laser pulse energies of 58.2,66.8,and 75.3μJ are,respectively,achieved with a minimum pulse width of<16.7 ns at a repetition rate of 10 kHz.Volumetric imaging of lipids is validated through scanning a fat beef slice with a PA microscopy system incorporated with the newly developed source,and a lateral resolution of 18.8μm and an axial resolution of 172.9μm are achieved.Moreover,the higher shooting speed of the developed source can potentially allow for increasing at twice the frame rate of current intravascular PA imaging.

Passively Q-switched erbium doped fiber laser using a gold nanostars based saturable absorber

In this paper, we propose and demonstrate an all-fiber passively Q-switched erbium doped fiber laser （EDFL） by using gold nanostars （GNSs） as a saturable absorber （SA） for the first time, to the best of our knowledge. In comparison with other gold nanomorphologies, GNSs have multiple localized surface plasmon resonances, which means that they can be used to construct wideband ultrafast pulse lasers. By inserting the GNS SA into an EDFL cavity pumped by a 980 nm laser diode, a stable passively Q-switched laser at 1564.5 nm was achieved for a threshold pump power of 40 mW. By gradually increasing the pump power from 40 to 120 mW, the pulse duration decreases from 12.8 to 5.3 its and the repetition rate increases from 10 to 17 kHz. Our results indicate that the GNSs are a promising SA for constructing pulse lasers.

Acousto-optic Q-switched cladding-pumped ytterbium-doped fiber laser

A diode-pumped, acousto-optic Q-switched fiber laser is presented based on multimode ytterbium-doped fiber. The fiber with core diameter of 30 μm is used to increase the laser gain volume and the pulse energy efficiently. The average power in excess of 9 W is obtained at the repetition rate of 20 kHz with 66% slope efficiency. The pulse width is 198 ns with no evident amplified spontaneous emission between pulses, thus the pulse energy and peak power are 465 μJ and 2.36 kW, respectively.