基于10m光子晶体光纤的放大自相似锁模振荡器研究

Amplifier similariton oscillator using 10 m photonic crystal fiber

基于单根10 m大模场面积保偏光子晶体光纤,搭建了带有色散图的放大自相似振荡器;通过仔细调节腔内色散量的大小以及位于色散补偿端的端镜前的狭缝位置和大小,实现了稳定的锁模运转,获得了抛物线形脉冲输出.输出脉冲的重复频率为8.6 MHz,脉冲宽度为6.2 ps,光谱宽度为3.84 nm,平均功率820 mW,对应单脉冲能量95 nJ.这是第一次在自相似振荡器中直接获得重复频率在10 MHz以下的脉冲输出,95 nJ也是目前自相似振荡器直接输出的最高脉冲能量.通过数值模拟证实了在第一个光栅的零级反射处和狭缝滤波后可以分别实现抛物线型脉冲和高斯脉冲的两种锁模脉冲输出.

Ultrashort pulse laser with a repetition rate of below 10 MHz is suitable for a variety of micromachining applications to avoid plasma shielding effects.Besides,the parabolic pulse possesses clean wings,short pulse duration,and large peak power because only the linear chirp is accumulated during the propagation.Based on these two points,a similariton oscillator with a repetition rate of below 10 MHz is a most perfect seed source of an amplification system for micromachining.In this paper,an amplifier similariton oscillator with dispersion map based on a piece of 10 m Yb-doped large-mode-area single-polarization photonic crystal fiber is demonstrated.The semiconductor saturable absorber mirror is employed in the linear cavity as an end mirror to initiate and maintain the mode-locking operation.An adjustable slit is adopted between the end mirror and grating pair in another arm,as a central wavelength adjuster and the spectral filter to ensure the laser operational wavelength in accordance with the working wavelength of semiconductor saturable absorber mirror and the stability of mode-locking operation.The stable single-pulse mode-locking operation can be achieved by adjusting the intracavity dispersion and the operating wavelength.With the net cavity dispersion of —0.89 ps2,a spectrum with steep and smooth edges is obtained,which means that the laser does not operate in the soliton regime but in the dispersion-mapped amplifier similariton regime.A highest output power of 820 mW is obtained with a pulse duration of 6.2 ps and spectral width of 3.84 nm under a pump power of 12.8 W.The repetition rate is8.6 MHz,corresponding to a pulse energy of 95 nJ.It is the first time that the similariton with a repetition rate of lower than 10 MHz and a highest pulse energy of 95 nJ from a similariton laser has been achieved,to the best of our knowledge.Numerical simulation results confirm that the self-similar evolution is achieved in the gain fiber,and the parabolic- and gauss-shaped pulse can be emitted at the zero-order reflection of the grating and after the slit,respectively.