注入噪声对光纤激光器锁模启动的影响

 从掺镱光纤激光器腔内的激光场出发，讨论了掺镱光纤激光器腔内的噪声信号对锁模启动的影响，并针对我们设计的8字腔超短脉冲光纤激光器进行了研究。通过对激光器腔内锁模过程的分析发现：在泵浦功率为214.75 mW时，自行研制的8字形腔掺Yb³⁺光纤激光器在未注入噪声信号时，输出端在30～50 s内获得稳定的锁模脉冲激光输出；在腔内注入脉宽30 ns，频率10 kHz，平均功率0.2 mW的脉冲噪声后，输出端在1~2 s内获得同样稳定的锁模脉冲激光输出。实验结果表明，注入激光器谐振腔内一定的噪声信号，可加速锁模的启动。     

孤子分子/类噪声脉冲可切换的混合锁模光纤激光器

不同类型脉冲之间的演化是被动锁模光纤激光器丰富动力学的体现。报道了一种可实现多种脉冲切换的混合锁模光纤激光器,当泵浦功率为400 mW时实现了孤子分子、谐波锁模、孤子簇之间的相互切换。增加泵浦功率至600 mW时获得了类噪声脉冲输出,对应的输出功率和单脉冲能量分别为15.2 mW和0.86 nJ。通过调节偏振控制器实现了类噪声脉冲中心波长从1 895 nm到1 930 nm可调谐。所搭建的激光器具有锁模脉冲可切换,波长可调谐,能自启动等优点。     

石墨烯被动锁模全正色散掺镱光纤激光器中的暗脉冲及其谐波

报道了一种基于石墨烯被动锁模的全正色散掺镱环形光纤激光器. 在激光器腔中应用激光诱导沉积法制备的石墨烯可饱和吸收体, 通过调节抽运光功率和偏振控制器的角度分别得到了明脉冲及其二阶谐波, 暗明脉冲对和暗脉冲及其二、三阶谐波这三类不同的脉冲. 其中, 暗明脉冲对和暗脉冲在基于石墨烯被动锁模的掺镱光纤激光器实验中都是第一次被观察到. 本文根据实验结果结合模拟分析了暗脉冲的产生机理, 并研究对比了明脉冲谐波和暗脉冲谐波产生的原因.     

氧化石墨烯被动锁模掺镱光纤激光器多脉冲现象的实验研究

利用氧化石墨烯作为可饱和吸收体,在被动锁模全正常色散掺镱光纤激光器中研究了多脉冲的现象,在同一抽运功率不同偏振态下,实验获得了矩形脉冲谐波锁模、耗散孤子谐波锁模、准谐波锁模,脉冲峰值周期性调制,脉冲簇、脉冲束、混沌多重脉冲的多脉冲现象,插入激光腔内的2nm窄带滤波器具有限制增益带宽、对脉冲塑形、诱导多脉冲产生的作用,调节偏振控制器相当于改变腔内增益,是实现不同类型多脉冲现象的主要原因,本实验研究有利于加深对多脉冲动力学行为在正常色散区域氧化石墨烯锁模掺镱光纤激光器中的理解。     

基于石墨烯的全光纤主动锁模激光器

利用光纤倏逝波耦合效应,设计了一种基于石墨烯全光纤结构的主动锁模激光器。该石墨烯全光纤锁模器件基于侧面腐蚀的单模光纤,构建了银/聚二甲基硅氧烷（PDMS）/石墨烯的电容型结构,腐蚀的单模光纤置于PDMS和石墨烯之间。实验结果显示,在电容结构两端施加与激光腔的共振频率一致及其整数倍的周期性方波电压信号,并对腔内光进行调制,可实现1558 nm光纤激光器的主动锁模。所设计的主动锁模激光器获得了基本频率及二次谐波的锁模脉冲,重复频率分别为12.2 MHz和24.4 MHz,实现了电控重复频率的脉冲输出。这种石墨烯全光纤锁模器件具有低成本、低功耗的优势,为实现灵活可控的主动锁模激光器提供了新思路。     

被动高阶谐波锁模掺Er3+光纤激光超短光脉冲的产生及其放大

报道了利用光纤的非线性偏振旋转效应产生可饱和吸收体的锁模机制,从掺Er3+光纤环形腔激光器中产生稳定的高阶谐波锁模光脉冲的实验研究结果(限于示波器带宽,实验中最高曾测量到稳定的407.6 MHz重复频率的谐波锁模光脉冲).实验中发现有三种不同的演化方式产生高阶谐波锁模光脉冲,还观察到在83.52 MHz谐波锁模光脉冲的光谱中出现孤子光谱边带.四阶谐波锁模(83.52 MHz重复频率)超短光脉冲经过6 m长高掺杂浓度的掺Er3+光纤放大器放大后产生了平均输出功率13.88 mW,脉宽201 fs,中心波长1.531 μm,单脉冲能量为0.166 nJ,对应的光脉冲峰值功率0.811×103 W,增益19 dB的放大结果.     

低阈值锁模状态可转换的全保偏光纤激光器

报道了一种可实现低阈值自启动的全保偏九字腔光纤激光器。谐振腔结构中使用相移器降低锁模阈值,当泵浦功率达到120 mW时,便可实现自启动的传统孤子锁模,中心波长为1530 nm,脉冲宽度为614.6 fs。随后泵浦功率逐渐增大到470 mW,实现了从孤子脉冲到类噪声脉冲的转换,在该锁模状态下的激光器输出功率为63.2 mW,对应的类噪声脉冲能量为5.69 nJ。所搭建的激光器具有低锁模阈值、自启动的优势,并且仅通过调节泵浦功率就能够实现超快脉冲和高能量脉冲间的转换,具有广泛的应用价值。     

被动高阶谐波锁模掺Er3+光纤激光超短光脉冲的产生及其放大

报道了利用光纤的非线性偏振旋转效应产生可饱和吸收体的锁模机制,从掺Er3+光纤环形腔激光器中产生稳定的高阶谐波锁模光脉冲的实验研究结果(限于示波器带宽,实验中最高曾测量到稳定的4076MHz重复频率的谐波锁模光脉冲).实验中发现有三种不同的演化方式产生高阶谐波锁模光脉冲,还观察到在8352MHz谐波锁模光脉冲的光谱中出现孤子光谱边带.四阶谐波锁模(8352MHz重复频率)超短光脉冲经过6m长高掺杂浓度的掺Er3+光纤放大器放大后产生了平均输出功率1388mW,脉宽201fs,中心波长1531μm,单脉冲能 关键词：     

抑制相位噪声实现主动锁模光纤激光器稳定工作

腔长漂移是引起主动锁模光纤激光器不稳定的一个主要原因。通过理论分析得出了主动锁模光纤激光器输出脉冲相位噪声和腔长漂移的关系，并采用抑制相位噪声的方法实现了主动锁模光纤激光器长达８小时的稳定工作。     

大色散稳定腔长的光纤锁模激光器的锁模特性研究

报道了一种新型的采用大色散腔结构的光纤锁模激光器,它可以有效地克服激光器腔长抖动对锁模的不良影响,同时,实验中发现,该结构对超模噪声也有很好的抑制作用。完成了大色散控制,电光调制器调制的,稳定的光纤锁模激光器实验,得到形状为sech^2的光脉冲输出,脉冲宽度为7.6ps,脉冲带宽积为0．335。     

Pulse-amplitude-equalized output from a rational harmonic mode-locked fiber laser

We report, for the first time to our knowledge, the demonstration of amplitude equalization of high-repetition-rate pulses generated from a rational harmonic mode-locked Er-doped fiber laser. The output pulses are injected into another fiber laser with a nonlinear optical loop mirror. This scheme provides pulse-amplitude equalization up to the ninth rational harmonic mode-locked pulse train.     

Stretched-pulse mode-locking synchronously triggered by a femtosecond master laser at sub-megahertz repetition rate

A stretched-pulse mode-locked ytterbium-doped fiber laser was passively synchronized to a femtosecond Ti:sapphire laser at a low repetition rate of 240 kHz through large cross absorption modulation along additional 1-m-long erbium-doped fiber. The synchronous fiber laser with an ultra-long fiber cavity could produce not only nanosecond flat-top pulses with tunable pulse duration but also Gaussian-shape stretched pulses with its minimum pulse duration of ∼450 ps as confirmed by cross-correlation measurement. When operating in the stretched pulse regime, the sub-nanosecond fiber laser could be synchronously triggered by the master injection with the cavity-length mismatch tolerance up to ∼7.8 cm and timing jitter less than 400 fs, confirming that the stretched-pulse mode-locking of the ultra-long slave fiber laser could be robustly controlled by cross absorption modulation effects in the erbium-doped fiber with appropriate femtosecond master injection.     

Multi-wavelength mode-locked Er/Yb Co-doped fiber laser with square nano-second pulse output

We report a multi-wavelength mode-locked Er/Yb codoped fiber laser with square nano-second pulse output, which is constructed with a “figure-of-eight” cavity structure. A section of polarization-maintaining Er/Yb co-doped double clad fiber was used as the gain medium and pumped by a fiber pigtailed multimode laser diode working at 975 nm via a multimode fiber combiner. Several megahertz repetition rate output pulses with peak power up to 9.2 W and pulse duration around several nanoseconds were obtained.     

Harmonic mode locking in a sliding-frequency fiber laser

We demonstrate a sliding-frequency mode-locked (SFM) erbium fiber laser generating 20 ps pulses with center wavelengths rapidly sweeping across a spectral range of 50 nm. Excess optical nonlinearity in the laser cavity leads to multipulsing, with a tendency to tight pulse bunching (<3 ns) at the fundamental cavity frequency of 25 MHz. The addition of a parallel optical delay line, with a path difference equal to a rational fraction of the cavity length, distributes the pulses uniformly across the entire cavity and achieves a harmonic SFM up to 1 GHz. The result establishes cavity nonlinearity as a critical design parameter for picosecond wavelength-swept lasers.     

Environmentally stable all-normal-dispersion femtosecond fiber laser

We demonstrate a mode-locked all-normal-dispersion ytterbium-doped fiber laser constructed with polarization-maintaining fibers. Spectral filtering of a chirped pulse in the cavity, along with a semiconductor saturable absorber, produce self-starting femtosecond mode-locked operation with large normal dispersion. Environmentally stable generation of 2 nJ and 300 fs pulses is achieved.     

Long-cavity passively mode-locked fiber ring laser with high-energy rectangular-shape pulses in anomalous dispersion regime

We report on a long-cavity passively mode-locked fiber laser in the anomalous dispersion regime. The nonlinear polarization rotation technique is employed to achieve mode locking. The output pulse from the fiber laser has a rectangular shape and a corresponding gaussian-shape spectral profile. Stable mode-locked pulses at a repetition rate of 278 kHz with single pulse energy as high as 715 nJ are obtained under equal bidirectional pumping power of 500 mW in cavity. The experimental results demonstrate that the passively mode-locked fiber laser operating in the anomalous regime can also realize a high-energy pulse, which is different from the conventional low-energy soliton pulse.     

Ultralow-jitter passive timing stabilization of a mode-locked Er-doped fiber laser by injection of an optical pulse train

The pulse timing of a mode-locked Er-doped fiber laser was stabilized to a reference pulse train from a Cr:forsterite mode-locked laser by all-optical passive synchronization scheme. The reference pulses were injected into a ring cavity of the fiber laser by using a 1.3-1.5 mum wavelength-division multiplexer. The spectral shift induced by cross-phase modulation between copropagating two-color pulses realizes self-synchronization due to intracavity group-delay dispersion. The rms integration of timing jitter between the fiber laser pulse and the reference pulse was 3.7 fs in a Fourier frequency range from 1 Hz to 100 kHz.     

Direct generation of a 10 GHz 816 fs pulse train from an erbium-fiber soliton laser with asynchronous phase modulation

By employing the technique of asynchronous mode locking, we have successfully demonstrated direct generation of stable 10 GHz 816 fs pulse trains with a supermode-suppression ratio >70 dB from a hybrid mode-locked Er-fiber laser. When the modulation frequency deviates from the cavity harmonic frequency by 15-40 kHz, stable femtosecond soliton pulses are formed. Our results demonstrate that asynchronous mode locking can act as an effective mechanism for achieving a shorter pulse width and for stabilizing high-repetition-rate pulse trains in soliton fiber lasers.