【作者】 张文启；

【导师】 王智勇；

【作者基本信息】 北京工业大学 ， 光学工程， 2011， 硕士

【摘要】 本文从理论和实验上对MOPA结构声光调Q掺镱全光纤激光器进行了研究并从实验上对其产生百纳秒量级超连续谱进行了研究。该MOPA结构声光调Q全光纤激光器可用作激光打标的光源,产生的超连续谱激光可用在光电对抗等领域。产生超连续谱,泵浦光通常用飞秒和皮秒脉冲,而用纳秒和连续光的研究较少,本文获得了百纳秒量级全光纤结构超连续谱激光,平均功率突破瓦级。首先以调Q光纤激光器的速率方程为基础,从理论上分析了泵浦功率、纤芯直径、增益光纤长度、输出透过率、光纤固有损耗对脉冲能量和脉冲宽度的影响。实验中,采用半导体激光器(LD)为泵浦源,掺镱光纤为增益介质,光纤光栅(FBG)为谐振腔镜、带尾纤的声光Q开关(AOM)为调制器,输出端熔接光隔离器构成了声光调Q全光纤激光器种子源。通过实验获得了重复频率10-34 kHz连续可调,中心波长1064 nm,重复频率11 kHz时,脉冲宽度150 ns;重复频率23 kHz时,脉冲宽度200 ns,3 dB谱宽2.029 nm,平均功率212 mW的种子源。种子源所得的实验结果与以速率方程为基础的理论分析相符合。理论分析与实验结果表明:增益光纤的长度、输出透过率等一定时,种子源输出的平均功率,随泵浦功率的增大而线性增大;泵浦功率,输出透过率一定时,存在使平均功率最大的最佳光纤长度,增益光纤长度变长或变短,平均功率都下降;增益光纤长度,泵浦功率一定时,存在使平均功率最大的最佳输出透过率,输出透过率变大或变小,平均功率均下降;泵浦功率,输出透过率一定条件下,重复频率增大或者增益光纤长度变长,脉冲宽度均增大。实验中观察到,在泵浦功率较小、重复频率较高时,输出的脉冲重复频率仅有所设置频率的1/2或者1/3,只有当泵浦功率超过一定阈值时,重复频率才能达到所设置的值。种子源输出脉冲的中心波长主要受光纤光栅的光谱特性影响,不随泵浦功率、重复频率、增益光纤长度的改变而发生明显变化。本文对种子源输出的激光脉冲进行了两级放大实验。一级放大器获得平均功率为3 W,重复频率10-34 kHz连续可调,中心波长为1064 nm的激光脉冲。在重复频率为11 kHz时,脉冲宽度为200 ns;重复频率为23 kHz时,脉冲宽度为250 ns,3 dB谱宽为2.322 nm。与种子源输出的激光脉冲相比,通过一级放大后,激光脉冲宽度稍有增大,3 dB谱宽稍有展宽,中心波长没有明显变化。在一级放大器输出功率为2.7 W时,把一级放大器输出激光进行二级放大。二级放大器获得了平均功率10 W,重复频率10-34 kHz连续可调,中心波长为1064 nm的激光脉冲。在重复频率为11 kHz时,脉冲宽度为250 ns;重复频率为23 kHz时,脉冲宽度为275 ns,3 dB谱宽为2.492 nm。通过二级放大后,激光脉冲宽度稍有增大,3 dB谱宽稍有展宽,中心波长没有明显变化。在放大级中,输出功率随泵浦功率增大基本线性增大。采用纳秒量级脉冲激光,获得全光纤超连续谱,平均功率突破瓦级,国内鲜有报道。以MOPA结构声光调Q全光纤激光器作为泵浦源,光子晶体光纤作为非线性介质,获得了百纳秒量级超连续光谱脉冲输出,光谱范围是600-1700 nm,重复频率10-34 kHz连续可调,在重复频率为23 kHz时,脉冲宽度为250 ns,平均功率为1.46 W。更多还原

【Abstract】 This paper studies on acousto-optic Q-switched Yb3+-doped all-fiber laser in master-oscillator power amplifier (MOPA) configuration in theory and experiment and using it to generate hundred nanoseconds supercontinuum in experiment. Acousto-optic Q-switched Yb3+-doped all-fiber laser in MOPA configuration can be used as the laser source of laser marking. The supercontinuum generated by the laser can be used in the electro-optical countermeasure field and so on. To generate supercontinuum, pump sources are usually used femtosecond or picosecond pulses. Researches on using continuous laser or nanosecond pulse to generate supercontinuum are less. The paper gets all-fiber hundred nanoseconds supercontinuum laser, which average power breaks watts.Firstly, based on rate equation theory of the Q-switched fiber laser, pulse energy and pulse width are analyzed versus the pump power, core diameter, the gain fiber length, the output transmission, fiber intrinsic loss.The seed source of acousto-optic Q-switched Yb3+-doped all-fiber is using diode laser (LD) as pump source, ytterbium-doped fiber as the gain medium, fiber Bragg grating (FBG) as resonator mirrors, acousto-optic Q-switch (AOM) as a modulator in experiment. The optical isolator is used at the output. Seed source obtains the adjustable repetition rate 10-34 kHz, the center wavelength of 1064 nm laser pulse. When the repetition rate is 11 kHz, the pulse width is 150 ns. When the repetition rate is 23 kHz, the pulse width is 200 ns, the 3 dB spectral width is 2.029 nm and the average power is 212 mW. Experimental results meet the theoretical analysis based on rate equations.From the experimental results and the theoretical analysis, we can get the conclusion. When the length of gain fiber and the output transmission are certain, the average power of the seed source increases linearly as the pump power increasing. When pump power and the output transmission are certain, the average output power increase beginning, then reach the max, and fall finally as the gain fiber length increases. When pump power and the length of gain fiber are certain, the average output power increase beginning, then reach the max, and fall finally as the output transmission increases. When pump power and the output transmission are certain, the pulse width increases as the repetition rate increases or the length of gain fiber becomes longer. In experiments, when the pump power is small and the repetition rate is high, the repetition frequency of the output pulse is 1/2 or 1/3 of the set frequency. Only when the pump power exceeds a certain threshold, the repetition rate achieves the set value. The center wavelength of seed source output pulse is mainly affected by the spectral characteristics of fiber gratings, not with the pump power, repetition rate, length of gain fiber in change, changes significantly.In experiment of this paper, the output of seed source is amplified by two stage amplifier. The first stage amplifier obtains the pulses of 3 W average power, 10-34 kHz repetition rate, 1064 nm center wavelength. When the repetition rate is 11 kHz, the pulse width is 200 ns. When the repetition rate is 23 kHz, the pulse width is 250 ns, the 3 dB spectral width is 2.322 nm. Compared with seed source, the laser pulse width and 3 dB spectral width of the first stage amplifier increases slightly, the center wavelength did not change significantly. When the output power of the first stage amplifier is 2.7 W, the output pulses are put into the second stage amplifier. The second stage amplifier obtains the pulses of 10 W average power, 10-34 kHz repetition rate, 1064 nm center wavelength. When the repetition rate is 11 kHz, the pulse width is 250 ns. When the repetition rate is 23 kHz, the pulse width is 275 ns, the 3 dB spectral width is 2.492 nm. Compared with the first stage amplifier, the laser pulse width of the second stage amplifier increases slightly, the center wavelength did not change significantly. In the amplifier, the output power increases basic linearly with pump power.Using nanosecond pulsed laser to obtain all-fiber supercontinuum, average power breaking watts, have not been reported in the domestic. In this paper, using acousto-optic Q-switched fiber laser based on MOPA structure as the pump source, the photonic crystal fiber as the nonlinear medium, the hundred nanoseconds supercontinuum pulses are obtained. The spectral range is 600-1700 nm, continuously adjustable repetition rate is 10-34 kHz. When the repetition rate is 23 kHz, the pulse width is 250 ns and the average power is 1.46 W.更多还原