Effects of Yb-doping on flux pinning properties in YBa_2Cu_3O_(7-δ)

The effects of Yb-doping on the critical current density(Jc) and the critical temperature(Tc) in YBa2Cu3O7-δ(YBCO) were investigated.Rietveld refinements of X-ray diffraction showed that Yb3+ ions had partly substituted Y sites in YBCO and the unit cell volume V decreased monotonically as x increasing.Although Tc almost had no change with increasing Yb-concentration,the increase of Jc occurred as a field was applied and displayed a maximum at x=0.08.We argued that the formation of nanometric inhomogeneity may lead to the enhancement of pinning force.

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.

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.

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.

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.

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.

An Efficient Single-Frequency Yb-Doped All-Fiber MOPA Laser at 1064.3 nm

An efficient narrow=linewidth single-frequency （SF） Yb-doped all-fiber master oscillator power amplifier （MOPA） laser operating at 1064.3 nm is demonstrated experimentally. A ring cavity SF fiber laser is used as the seed source for the MOPA system and the Yb-doped fibers are employed as the gain medium or the saturable absorber. The SF operation is observed to be stable without mode hopping. The highest output power of 266 mW is obtained under the 400row pump power with the corresponding slope efficiency of 66.2-. The Hnewidth of the amplified output laser is approximately I kHz and its optical signal-to-noise ratio is over 45 dB.

Wideband All-Polarization-Maintaining Yb-Doped Mode-Locked Fiber Laser Using a Nonlinear Optical Loop Mirror

We report on a wide-band and stable mode-locked all-polarization-maintaining fiber laser configuration using a nonlinear optical loop mirror. The central wavelength of the laser is 1080.14nm and the 3dB bandwidth is 20.29nm. The repetition rate of the pulse is 3.28 MHz and the pulse width is 848ps. By tuning the pump power, which is centered at 980nrn, from 300mW to 380mW, we obtain a linearly changed output power from 6row to 7.12roW. The all-polarization-mMntaining fiber configuration is fundamental to the stability of the output power.

A 980 nm Yb-doped single-mode fibre laser with 946 nm Nd:YAG laser as pump source

Based on rate equations, this paper gives expressions of the output power, the pump power threshold, the slope efficiency, the fibre optimal length and the laser gain of a quasi-three-level Yb-doped fibre laser. The gain relationship between quasi-three-level system and four-level system is also given, which provides a theoretical basis for suppressing the four-level transmissions. In the experiment, we adopt the backward pumping configuration and use a linear cavity. The Yb-doped fibre laser has an output power of 372 mW of single-mode laser emission at 980 nm with a slope efficiency of 21.2% when the fibre length is 29.5 cm close to an optimal fibre length in theory. The experimental results accord well with the theoretical analyses.

Synthesis and Crystal Structure of Yb-doped S-FAP

To abtain large crystals for improving the physical and optical properties of materials, the crystal of Yb-doped S-FAP was sythesized by the Czochralski method, the growth process was analyzed, and its structure was determined. This material was confirmed to have a hexagonal structure, unit-cell parameters （a=b-0.9683（4） nm, c=0.7277（4） nm） are slightly different from the crystal parameters of S-FAP reported before.

Experimental Investigation of Wavelength-Tunable All-Normal-Dispersion Yb-Doped Mode-Locked Fiber Lasers:Compression and Amplification

Wavelength-tunable ultrashort pulse source with high energy is highly desired for a lot of applications. The wavelength-tunable all-normal-dispersion （ANDi） mode-locked fiber laser, which can be compressed easily and amplified by an all-fiber structure, is a promising seed of such a source with compact structures. The pulse compression and amplification at different center wavelengths （from 1026 to 1058nm） of the tunable ANDi Yb- doped mode-locked fiber lasers that we previously proposed are experimentally investigated in this work. It is found that, for different wavelengths, the duration and chirp of the direct output pulse from the oscillator vary considerably, however, the duration of compressed pulse fluctuates less. For the amplification process, due to the unf/at gain spectrum of Yb-doped fiber, the gain at a short wavelength is larger than that at a long wavelength. Consequently, the trends of spectrum distortions induced by the amplification process are different for different wavelengths. These results and analyses will be helpful for the design of a high-energy and wavelength-tunable ultrashort pulse source based on an ANDi seed.

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.

Theoretical and Numerical Study of Stress and Thermo-Optic in Photonic Crystal Fiber Laser in Different Pump Schemes

In this paper, we present a study of thermal, average power scaling, change in index of refraction and stress in photonic crystal fiber lasers with different pump schemes: forward pump scheme, backward pump scheme, forward pump scheme with reflection of 98%, backward pump scheme with reflection of 98% and bi-directional pump scheme. We show that management of thermal effects in fiber lasers will determine the efficiency and success of scaling-up efforts. In addition, we show that the most suitable scheme is the bi-directional.

Comparative Study of the Birefringence in Photonic Crystal Fiber Lasers

In this paper, we study the birefringence in photonic crystal fiber lasers PCFs and in conventional fiber lasers in the bi-directional pump scheme in the linear cavity laser. We show that the value of birefringence in photonic crystal fibers is smaller than that of conventional fiber lasers [1].

Radiation-induced change of OH content in Yb-doped silica glass

Yb-doped silica glasses containing low, medium, and high content of OH arc prepared through nanoporous glass sintering technology. High-OH sample exhibits better X-ray irradiation resistivity than low- and medium-OH samples. After irradiation, OH content of low- and medium-OH samples increases 37.5% and 11%, respectively; in contrast, OH content of high-OH sample decreases dramatically. The different OH content changes among the samples are discussed regarding the proposed inter-conversion reactions involving Si-H and Si-OH during the irradiation.

Generation of 8.5-nJ pulse from all-fiber dispersion compensation-free Yb-doped laser

We report the generation of an 8.5-nJ chirped pulse from a mode-locked all-fiber Yb-doped laser. Mode- locking is achieved through nonlinear polarization evolution （NPE） along with spectral filtering. The laser delivers 135 mW of average output power with positively chirped 10.9-ps pulses. The pulse repetition rate is 15.9 MHz, which results in an energy of 8.5 nJ per pulse. The externally dechirped pulse duration is 223 fs, and the pulse energy is 6 n J, which corresponds to the peak power of -27 kW.

Generation of few-cycle laser pulses by coherent synthesis based on a femtosecond Yb-doped fiber laser amplification system

We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle.By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.

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.

Power-scaled dissipative soliton using double-cladding-pumped Yb-doped all-fiber amplifier

We report on an all-fiber oscillator followed by an all-fiber amplifier to produce as short as 382 fs laser pulses with up to 0.9 W average power. The oscillator is an all-normal-dispersion all-fiber dissipative soliton laser operating at1030 nm, and operating in dissipative soliton mode. The amplifier stage is mainly based on a double-cladding20 μm radius ytterbium-doped fiber pumped by an up to 2.5 W CW laser source. The optical-to-optical conversion amplifier efficiency is around 40%. To our knowledge, this is the first report of an all-fiber mode-locked fiber laser oscillator amplified by an all-fiber amplifier.