Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.     

Passively Q-switched dual-wavelength Yb:LSO laser based on tungsten disulphide saturable absorber

We demonstrate a passively Q-switched Yb:LSO laser based on tungsten disulphide(WS_2) saturable absorber operating at 1034 nm and 1056 nm simultaneously. The saturable absorbers were fabricated by spin coating method. With low speed, the WS_2 nanoplatelets embedded in polyvinyl alcohol could be coated on a BK7 glass substrate coated with high-refractive-index thin polymer. The shortest pulse width of 1.6 μs with a repetition rate of 76.9 k Hz is obtained. As the pump power increases to 9 W, the maximum output power is measured to be 250 m W, corresponding to a single pulse energy of 3.25 μJ. To the best of our knowledge, this is the first time to obtain dual-wavelength Q-switched solid-state laser using few-layer WS_2 nanoplatelets.     

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.     

Er-doped all-fiber laser mode-locked by graphitic carbon nitride nanosheets

Few-layer graphitic carbon nitride(g-C_3N_4) nanosheets were fabricated and utilized as a saturable absorber for mode-locking in an Er-doped fiber laser with net normal dispersion. The g-C_3N_4/polyvinyl alcohol(PVA) hybrid-film-based saturable absorber has a modulation depth of 4.01% and a saturation intensity of 7.5 MW/cm~2. By integrating g-C_3N_4-PVA mode-locker into the laser cavity, a mode-locked operation could be obtained. The achieved mode-locking pulse centered at 1530.3 nm has a pulse width of 530 ps. Its repetition rate is 40.8 MHz, and the corresponding signal-to-noise ratio is about 55 dB.     

基于目标反射回光对高功率光纤激光器影响的理论模型和数值研究

在高功率光纤激光系统中,常会出现激光照射到目标处产生的回光被重新耦合到激光器内部并得到放大,从而损伤激光系统的现象.对于高功率光谱合成光纤激光系统等缺乏有效回光防护的高功率激光系统,该情况尤为严重.为了解决上述问题,有必要综合整个系统链路中的多种物理效应,评估和分析反射回光对系统运转状态的影响,在设计光纤激光器时优化光路布局和系统结构,以尽量避免不必要的损失.本文基于大气传输理论、光纤速率方程和介质热传导方程模型,分析了反向回光对高功率光纤激光器的影响.研究发现,在大气条件一定的情况下,回光功率与传输距离、光轴偏移角度、光束发散角和光束中心位置偏移量等因素有关,并且会影响光纤激光器输出功率、光束质量因子、热效应和受激拉曼散射光谱信噪比.研究结果对于优化高能光纤激光系统的外光路布局和激光器内部器件系统参数设计具有一定的指导意义.