增益开关线偏振单频脉冲光纤激光器

Gain switched linearly polarized single-frequency pulsed fiber laser

报道了一台线偏振单频脉冲光纤激光器.采用全保偏环形腔结构搭建全光纤振荡器,在腔内熔接一段未抽运的保偏掺镱光纤作为饱和吸收体,产生超窄带的动态光栅进行滤波选模,实现了激光器的单频输出.利用976 nm半导体激光器作为抽运源,产生脉冲加连续的混合抽运激光,实现了重频10—90 kHz、脉宽1—8μs的长脉冲输出.实验研究了抽运功率和重复频率等参数对输出激光的时域、频域和功率特性的影响.实验发现输出激光的频域特性在一定功率范围内存在光学双稳态现象,分析了激光功率特性对动态光栅选模机制的影响.通过参数优化,最终实现了中心波长1064 nm、线宽约23.5 MHz、重频10—90 kHz、脉宽4—8μs、偏振消光比约29 dB的单频脉冲激光输出.

Single-frequency pulsed fiber lasers have aroused intense interest due to their excellent performances in terms of good coherence,compact structure and good beam quality,which have been widely used in different areas,such as coherent LIDAR,nonlinear frequency conversion,and remote sensing.In this paper,a linearly polarized single-frequency pulsed fiber laser is reported.The narrow linewidth all-fiber oscillator is built by using an all-polarization-maintaining ring cavity structure.A section of unpumped polarization-maintaining ytterbium doped fiber is fused in the cavity as a saturated absorber to produce ultra-narrow bandwidth dynamic grating,which can be used for longitudinal mode selection.Thus,the laser can realize single-frequency operation.A 976-nm semiconductor laser is used as a pump source to generate a hybrid pump laser,which contains both pulsed component and continuous component.As a result,a long-pulse laser is achieved with a repetition rate of 10-90 kHz and a pulse duration of 1-8 μs.At the same time,the effects of pump power and repetition rate on the time domain,the frequency domain and the power characteristics of the output laser are investigated.It is found that there is an optical bistability in the frequency domain characteristic of the output laser within a certain power range.And the influence of the laser power characteristic on the longitudinal mode selection mechanism of dynamic grating is analyzed.Finally,through parameter optimization,single-frequency pulsed fiber laser is achieved with a center wavelength of 1064 nm,a linewidth of about 23.5 MHz,a repetition rate of 10-90 kHz,a pulse duration of 4-8 μs,and a polarization extinction ratio of about 29 dB.