Stimulated Brillouin Scattering Enhancement Factor Improvement in a 11.6-GHz-Linewidth 1.5-kW Yb-Doped Fiber Amplifier

The stimulated Brillouin scattering （SBS） threshold enhancement factor in a pure white noise linewidth broad- ening Yb-doped fiber amplifier （YDFA） with a short large mode area fiber is theoretically and experimentally studied. We demonstrate a 1064.08nm, 11.6 GHz finewidth, 1.5 k W output power YDFA with an SBS threshold enhancement of -57 （26 W SBS threshold with single frequency seed）. The output beam is near-diffraction lim- ited with a beam quality factor elM2 = 1.15 and a slope efficiency of up to 87%. No SBS or stimulated Raman scattering effects are observed in the whole power range. Further power sealing is limited by the available pump power in our system.

Tunable and Switchable Narrow Bandwidth Semiconductor-Saturable Absorber Mirror Mode-Locked Yb-Doped Fiber Laser Delivering Different Pulse Widths

The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror （SESAM）. Two narrow-band fiber Bragg gratings centered at 1029.9nm and 1032nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9nm and 1032nm. The laser delivers different pulse widths of 7.5ps for 1030nm and 20ps for 1032nm. The maximum output power for both could reach -6.5mW at single pulse operation. The output wavelength couM be tuned to about 0.gnm intervals ranging from 1030.2nm to 1031.1 nm and from 1032.15nm to 1033.7nm with the temperature change of the fiber Bragg grating, respectively.

Generation of Broadband Spectrum from a Simple Nonlinear-Polarization-Evolution Mode-Locked Yb-Doped Fiber Oscillator

We demonstrate a nonlinear polarization evolution mode-locked Yb-doped fiber oscillator with the broadband spectrum output operating in a dispersion-managed regime. Pumped by a 976 nm single-mode laser diode, stable mode-locked ultrashort pulses are emitted with an average power of 198mW at a repetition rate of 124MHz, corresponding to a pulse energy of 1.6nJ. The output spectrum spans from 950nm to ll50nm so that the transform-limited pulse duration is as short as 23 fs. Due to the imperfect dispersion compensation, we compress the pulses to 32 fs in this experiment.

Passively Q-Switched Yb-Doped Fiber Laser Operating at 1.06 μm with Two-Dimensional Silver Nanoplate as Saturable Absorber

A two-dimensional silver nanoplate is prepared with the seed-mediated growth method and is used for achieving pulse fiber laser operation. By controlling the dimension parameters of the silver nanoplate, the surface plasmon resonance absorption peak of the material is successfully adjusted to 1068 nm. Based on the silver nanoplate as a saturable absorber, a passively Q-switched Yb-doped fiber laser operating at 1062 nm is demonstrated. The maximum average output power of 3.49mW is obtained with a minimum pulse width of 1.84#s at a pulse repetition rate of 65.TkHz, and the corresponding pulse energy and peak power are 53.1 nJ and 28.8mW, respectively.

High Power Passive Phase Locking of Four Yb-Doped Fiber Amplifiers by an All-Optical Feedback Loop

We report the passive phase locking of four high power Yb-doped fiber amplifiers with ring cavity.The interference patterns at different output power are observed and the Strehl ratios are measured.The maximum coherent output power of the fiber array is up to 1062 W by multi-stage amplification.The stable beam profiles of various phase relationships are observed by controlling the position of the feedback fiber,in good agreement with the calculated results.By using master oscillator power-amplifier(MOPA)architecture and broadband operation of passively phased systems,higher power scaling with high beam quality appears to be feasible.

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.

Low-repetition-rate, all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber

A low-repetition-rate, all-polarization-maintaining（PM）-fiber sub-nanosecond oscillator is presented, which is simple and low-cost, composed of standard components. The ring cavity is elongated by 114-m-long standard PM fiber, and passively mode-locked by a fiber pigtailed semiconductor saturable absorber. Linearly polarized pulses with 1.66 MHz repetition rate and 22 dB polarization extinction ratio are generated at a wavelength of 1030 nm, which is determined by an intracavity filter. In addition, to demonstrate that the oscillator is a good seed for high energy pulse generation, an all-fiber master oscillator power amplifier is built and amplified pulses with energy about 2 μJ are obtained.

Characteristics of Soliton Evolution in the Wave-Breaking-Free Regime in a Passively Mode-Locked Yb-Doped Fiber Laser

We focus on several aspects concerning the numerical simulation of a passively mode-locked Yb-doped fiber laser by a non-distributed model.The characteristics of soliton evolution in a wave-breaking-free regime are numerically investigated with the split-step Fourier method.Based on the model,a parabolic-shaped soliton with a nearly linear chirp and bound soliton pairs are obtained by controlling the intra-cavity average dispersion of the fiber laser.A phenomenon is observed that by keeping the system parameters unchanged,linearly chirped parabolic soliton and bound soliton pairs are attainable under different initial conditions in the transient region between these two kinds of solitons.

Pump-induced carrier envelope offset frequency dynamics and stabilization of an Yb-doped fiber frequency comb

In this paper, we demonstrate a carrier envelope phase-stabilized Yb-doped fiber frequency comb seeding by a nonlinear-polarization-evolution（NPE） mode-locked laser at a repetition rate of 60 MHz with a pulse duration of 191 fs.The pump-induced carrier envelope offset frequency（ f0） nonlinear tuning is discussed and further explained by the spectrum shift of the laser pulse. Through the environmental noise suppression, the drift of the free-running f0 is reduced down to less than 3 MHz within an hour. By feedback control on the pump power with a self-made phase-lock loop（PLL）electronics the carrier envelope offset frequency is well phase-locked with a frequency jitter of 85 m Hz within an hour.

Generation of multi-wavelength square pulses in the dissipative soliton resonance regime by a Yb-doped fiber laser

Multi-wavelength square pulses are generated in the dissipative soliton resonance(DSR) regime by a Yb-doped fiber laser(YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters,a multi-wavelength DSR pulse can be generated in single-and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering(SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs.

NOLM-based Mode-locked Yb-doped Fiber Laser with Wide-spectrum

In this paper,a mode-locked Ytterbiumdoped fiber laser based on nonlinear optical loop mirror(NOLM)is proposed.The laser generates a wide-spectrum dissipative soliton resonance modelocked pulse with strong stimulated Raman scattering.The fiber laser is pumped forward,and the fiber ring cavity contains double-cladding Yb-doped fiber,output coupler,polarization controller,polarization independent isolator and other elements.NOLM is connected with the ring cavity by through a 3dB beam splitter and 25m single-mode fiber.The total length of the eight-shape cavity laser is about 60meters.By adjusting the intra-cavity polarization controller,a stable dissipative soliton resonance mode-locked spike pulse can be achieved.The repetition frequency of the pulse train is 3.44MHz,which is consistent with the cavity length.The 3dB bandwidth of the spectrum reaches 70.6nm,and the 10dB bandwidth is close to 147.11nm.In this experiment,dissipative soliton resonance mode-locked pulses with wide spectrum and high pulse energy are realized by a traditional modelocking method,which has wide application in many fields such as laser spectral detection and terahertz wave generation.

Environmentally stable,spectral-shape-controllable,GHz femtosecond Yb-doped fiber laser

We demonstrate an all-polarization-maintaining[PM]passively mode-locked Yb^(3+)-doped fiber laser[YDFL]with a fundamental repetition rate of 1.3 GHz.The optical spectra of a linearly polarized soliton exhibit different shapes by rotating the fast axis of the fiber optical pigtail of a dispersive dielectric mirror.The oscillator provides a series of laser performance,such as a threshold pump power for continuous wave laser oscillation of 3.1 mW,an optical-to-optical efficiency for modelocking of 29%,and an integrated relative intensity noise of 0.08%.To the best of our knowledge,this is the first report of>1 GHz ultrafast all-fiber YDFL with PM architecture.

Wavelength-tunable dissipative soliton from Yb-doped fiber laser with nonlinear amplifying loop mirror

We report a Yb-doped mode-locked fiber laser based on a nonlinear amplifying loop mirror[NALM],which is all-normaldispersion[ANDi],and allows the output wavelength to be tunable.The laser can generate a stable femtosecond dissipative soliton with a maximum output power of 196 mW.Its repetition rate is 112.4 MHz,and the final pulse duration is 236 fs.By adjusting the angle of the reflective diffraction grating,the mode-locked fiber laser was realized to tune the output with a tuning range of 54 nm from 1011.8 nm to 1065.6 nm.To the best of our knowledge,this is the widest tuning range of an ANDi Yb-doped mode-locked fiber laser based on NALM.

A theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers

We report on a theoretical and experimental study of an all-normal-dispersion （ANDi） Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation （NPR） is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schr6dinger （CNLS） equation, a model simulating the mode-locked process of an all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller （PC） along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.

73 nJ, 109 fs Yb-doped fiber laser at 19 MHz repetition rate in amplifier similariton regime

We report femtosecond pulse generation in an amplifier similariton oscillator and a prechirped fiber amplifier system. The final output power is 1.4W, and the fundamental repetition rate is 19.1 MHz after a single state fiber amplifier. The pulsewidth is 109 fs.

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier

A 980-nm semiconductor saturable absorber mirror（SESAM） mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 m W and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-m W maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission（ASE） nor harmful oscillation around 1030 nm is observed. Moreover,through a two-stage all-fiber-integrated amplifier, an output power of 740 m W is generated with a pulse width of 200 ps.

Linearly polarized operation of Yb-doped fiber laser by Brewster's angle-polished fiber end

A new method to obtain linear polarization operation by Brewster＇s angle-polished fiber end is demonstrated. By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity, a cladding-pumped linear polarization and single-transverse-mode （M2 〈 1.1） Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm （FWHM） is less than 0.2 nm, is obtained in a simple configuration. The output power is up to 10 W which is continuous- wave output at 1085 nm, and the slope efficiency is 63% with respect to the coupled pump power and 75% with respect to the absorbed pump power, respectively. The measured 21-dB polarization extinction ratio does not degrade with the output power. The simplicity of such an approach is highly beneficial for a number of applications, including the use of a fiber laser for the nonlinear wavelength conversion （especially for the intracavity frequency doubling） and for the coherent and spectral beam combination.

MoS2 saturable absorber for single frequency oscillation of highly Yb-doped fiber laser

In this Letter, a single-frequency fiber laser using a molybdenum disulfide （MoS2） thin film as a saturable absorber is demonstrated. We use a short length of highly Yb-doped fiber as the gain medium and a fiber ferrule with MoS2 film adhered to it by index matching gel （IMG） that acts as the saturable absorber. The saturable absorber can be used to discriminate and select the single longitudinal modes. The maximum output power of the single-frequency fiber laser is 15,3 mW at a pump power of 130 mW and the slope efficiency is 15.3%. The optical signal-to-noise ratio and the laser linewidths are -60 dB and 5.89 kHz, respectively.

“Periodic”soliton explosions in a dual-wavelength mode-locked Yb-doped fiber laser

We report the"periodic"soliton explosions induced by intracavity soliton collisions in a dual-wavelength modelocked Yb-doped fiber laser.Owing to the different group velocities of the two wavelengths,the mode-locked solitons centered at different wavelengths would periodically collide with each other.By using the dispersive Fourier transformation technique,it was found that each collision would induce soliton explosions,but none of them would be identical.Therefore,this phenomenon was termed as"periodic"soliton explosions.In addition,the dissipative rogue waves were detected in the dual-wavelength mode-locked state.The experimental results would be fruitful to the communities interested in soliton dynamics and dual-comb lasers.

Strigolactones modulate cotton fiber elongation and secondary cell wall thickening

Cotton is one of the most important economic crops in the world,and it is a major source of fiber in the textile industry.Strigolactones(SLs)are a class of carotenoid-derived plant hormones involved in many processes of plant growth and development,although the functions of SL in fiber development remain largely unknown.Here,we found that the endogenous SLs were significantly higher in fibers at 20 days post-anthesis(DPA).Exogenous SLs significantly increased fiber length and cell wall thickness.Furthermore,we cloned three key SL biosynthetic genes,namely GhD27,GhMAX3,and GhMAX4,which were highly expressed in fibers,and subcellular localization analyses revealed that GhD27,GhMAX3,and GhMAX4 were localized in the chloroplast.The exogenous expression of GhD27,GhMAX3,and GhMAX4 complemented the physiological phenotypes of d27,max3,and max4 mutations in Arabidopsis,respectively.Knockdown of GhD27,GhMAX3,and GhMAX4 in cotton resulted in increased numbers of axillary buds and leaves,reduced fiber length,and significantly reduced fiber thickness.These findings revealed that SLs participate in plant growth,fiber elongation,and secondary cell wall formation in cotton.These results provide new and effective genetic resources for improving cotton fiber yield and plant architecture.