多模光纤光栅温度传感特性的实验研究

利用氢敏化处理的多模光纤制作了多模光纤光栅,并对多模光纤光栅的温度传感特性进行了实验研究与理论分析,表明这种光栅三个反射峰的布拉格波长随温度变化均呈现出良好的线性关系,并且重复性相当好,同一光栅的各反射峰的理论温度灵敏度系数都等于0．01nm／℃,实验测得的温度灵敏度系数为0．0098nm／℃或0．0099nm／℃,与理论分析相当吻合,这些特性与单模光纤光栅的温度传感特性接近相同。因此可以用多模光纤光栅代替单模光纤光栅开发光纤光栅传感器,以降低成本;这一实验结果还可以作为对多模光纤光栅进一步深入研究的参考。     

被动谐波锁模掺Yb3+光纤环形激光器

 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Yb³⁺光纤环形激光器中得到稳定高阶谐波锁模光脉冲。理论分析了工作于正色散区的掺Yb³⁺光纤环形激光器的特性。实验中观测到了掺Yb³⁺光纤环形激光器3种不同演化方式产生高阶锁模光脉冲。4阶谐波锁模脉冲（107.2 MHz重复频率）经过1 m长高掺杂Yb³⁺光纤放大器放大后产生了平均功率100 mW，脉宽22.8 ps的脉冲，最后经过光栅压缩得到了平均输出功率20 mW，脉宽307 fs，脉冲中心波长1 051.2 nm，带宽13.76 nm的激光。     

被动锁模Yb3+光纤环形腔激光器的研究

 采用974 nm半导体激光器作为泵浦源，超高掺杂Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到稳定的ps量级锁模光脉冲。泵浦功率220 mW时，激光器锁模阈值功率150 mW，输出功率26 mW，锁模光脉冲中心波长1 046 nm，3 dB带宽6.01 nm，20 dB带宽16 nm，脉宽22 ps，重复频率20 MHz。与同类光纤激光器相比，该激光器输出功率高，具有更好的稳定性。     

自启动被动锁模掺铒光纤激光器的研究

在非线性光纤环形镜非线性开关效应和块状半导体波导饱和吸收效应的共同作用下，实现了掺铒光纤激光器的自启动被动锁模，获得了十分稳定的锁模脉冲序列，观察到高次谐频锁模脉冲输出。分析了非线性光纤环形镜的非线性开关反射特性。     

Gigahertz Harmonic Mode-Locked Fiber Laser Based on Tunable SMS Ultrafast Optical Switch

A novel passively gigahertz harmonic mode-locked all-fiber laser based on hybrid fiber structure (single-mode fiber–graded-index multimode fiber–single-mode fiber (SMS)) is proposed SMS, which coils on the paddles of polarization controller (PC), is demonstrated to modulate the temporal intensity for mode-locking. The nonlinear absorption properties of the optical switch are controllable by adjusting the paddles of PC; such an ultrafast optical switch enables the wavelength switchable harmonic mode-locking operation. Ultrafast pulses with 1.9 ps at 1558.41 nm and 0.95 ps at 1563.08 nm are generated. The maximum repetition rate of the laser up to 1.127 GHz harmonic of fundamental repetition mode-locking at 1563.08 nm, corresponding to 880 order, and the output power is 4.2 mW. Considering its superiority in terms of low cost, easy integration, and high reliability, the findings validate that SMS can be used in harmonic mode-locking.     

飞秒被动锁模环形腔掺Er3＋光纤激光器

在考虑增益、损耗、群速度色散、自相位调制、快速可饱和吸收体等各种参数同时作用情况下，分析了非线性偏振旋转效应自启动锁模机理，研究了腔体参数与锁模脉冲之间的关系，并给出飞秒被动锁模环形腔掺Er3＋光纤激光器实验原理。实验采用性能稳定的980nm半导体激光器作为抽运源，高掺杂短长度掺Er3＋光纤作为增益介质，利用非线性偏振旋转锁模技术，得到了稳定的飞秒自起振锁模光脉冲。抽运功率为23mW时，激光器输出锁模脉冲中心波长1552nm，3dB带宽为7.6nm，重复频率14.0MHz，平均输出功率0.43mW，自起振锁模泵浦阈值功率11.5mW,并观测到了稳定的高阶锁模脉冲输出。该激光器与报道过的相同结构光纤激光器相比,自起振泵浦阈值低、脉冲能量高、稳定性好，且频谱边带幅度小。     

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.     

全光纤超短脉冲掺Yb3+光纤环形激光器

讨论了自启动被动锁模掺Yb³⁺光纤环形激光器产生短脉冲的机理，并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.采用两个976nm半导体激光器级联抽运作为抽运源，高掺杂浓度掺Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到自启动、十分稳定的ps量级锁模光脉冲.激光器锁模阈值功率260mW，输出功率25mW，锁模光脉冲中心波长1056nm，3dB带宽11.7nm，重复频率20MHz.与其他结构光纤激光器相比，这种全光纤结构具有更高的效率和更好的稳定性. 关键词： 环形光纤激光器 3+光纤')" href="#">高掺杂浓度掺Yb³⁺光纤 自启动 被动锁模     

利用锁模光纤激光器在色散位移光纤中产生超连续谱的研究

采用主动锁模光纤激光器输出的重复频率10GHz、脉宽7．97ps的脉冲作为抽运光源,无需压缩后直接抽运4．2km的普通色散位移光纤(DSF)．利用色散位移光纤中自相位调制、交叉相位调制等非线性效应的联合作用,获得了20dB带宽达125nm、覆盖整个C波段、L波段和部分S波段的超连续(SC)谱。实验研究了抽运光脉冲峰值功率和抽运波长对超连续谱宽度的影响,结果表明抽运光脉冲峰值功率越高,得到的超连续谱的带宽越宽;通过对抽运波长的优化,可以实现最大程度的超连续展宽;分析了滤波器带宽对脉冲质量的影响;利用0．4nm带宽的可调谐滤波器对从超连续谱中滤出脉冲的特性进行了研究,在超连续谱的不同波长处获得了脉宽为8．90～9．80ps、时间一带宽积为0．44～0．49的稳定的窄光脉冲。     

Impacts of operational parameters on nonlinear polarization rotation-based passively mode-locked fiber laser

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper.The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shro¨dinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser.The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power.The periodicity of the polarization controlling is observed.With given pump power,there exists a set of polarization controlling under which the ultra-short pulse can be generated.With given polarization controlling,the mode-locked state can be maintained generally except for some particular values of pump power.Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes.The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.     

基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器

报道了一种基于石墨烯可饱和吸收体的纳秒锁模掺铥光纤激光器.该激光器采用环形腔结构,利用自制的三层石墨烯薄膜作为可饱和吸收体实现锁模.同时在腔内插入一个窄带光纤光栅,约束腔内起振的纵模数,适当调节抽运功率和偏振控制器的角度,得到了重复频率为3.8 MHz、脉宽在3.8—94.3 ns之间灵活可调的2μm纳秒锁模脉冲输出,整个脉宽调节范围超过90 ns.此外,由于获得的兆赫兹纳秒锁模脉冲时间带宽积在49—1119范围内,即存在强烈的啁啾,因而可作为2μm波段啁啾脉冲放大系统中的种子源使用.     

Generation of cavity-birefringence-dependent multi-wavelength bright–dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright–dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL). The nonlinear polarization rotation(NPR) and nonlinear optical loop mirror(NOLM) were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation. By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF), the fiber laser could operate stably in a multi-wavelength emission state. Compared with the absence of the PMF, the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright–dark pulse pair.     

Influence of the bias current on the output characteristics of a mode-locked fiber ring laser consisting of two SOAs

In this paper, after obtaining the mode-locked pulse shape with self-reproduction theory, the influence of the bias current on the output characteristics of a backward-optical-injection harmonic mode-locked fiber ring laser consisting of two semiconductor optical amplifiers (SOAs) has been numerically investigated. The results show that the mode-locked pulse with high peak power and narrow width can be obtained through reasonably adjusting the bias currents of the two SOAs.     

Stable multiwavelength and passively mode-locked Yb-doped fiber laser based on nonlinear polarization rotation

Based on the nonlinear polarization rotation (NPR) technique and a fiber Mach–Zehnder interferometer (MZI), a fiber laser which can work in two different modes has been demonstrated. In one mode, it works as a continuous wave (CW) multiwavelength laser, and stable dual-, triple- and tetra-wavelength lasing with the wavelength spacing of 1.1 nm are obtained. In the other mode, it works as a passively mode-locked fiber laser, and the generated pulses have a repetition rate of 10.6 MHz, an FWHM width of 800 ps and the largest energy of 1 nJ. The multi-functional property makes this fiber laser a very convenient, cost effective and multi-purpose laser source.     

Spectral broadening of a multimode continuous-wave optical field propagating in the normal dispersion regime of a fiber

We investigate experimentally and theoretically the broadening of the optical spectrum of a multimode cw field propagating in the normal dispersion regime of a single-mode fiber. The width of the optical spectrum is not a monotonic function of propagation length. This behavior arising from the interplay between the Kerr effect and group-velocity dispersion contrasts with spectral broadening of mode-locked pulses.     

2-μm mode-locked nanosecond fiber laser based on MoS_2 saturable absorber

We demonstrated a 2-μm passively mode-locked nanosecond fiber laser based on a MoS_2 saturable absorber(SA).Owing to the effect of nonlinear absorption in the MoS_2 SA, the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W. The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm, respectively. Experimental results show that MoS_2 is a promising material for a 2-μm mode-locked fiber laser.     

8字形腔波长可调谐锁模脉冲光纤激光器

采用非线性光纤环形镜加脉冲锁模技术及可调谐光纤光栅滤波器,对8字形腔被动锁模掺铒光纤激光器进行了波长可调谐输出的实验研究.在EDFA抽运光功率一定的情况下,通过调节偏振控制器和可调谐光纤光栅滤波器,获得了光谱稳定、重复频率1.1 MHz、输出功率起伏小于0.8 dBm、中心波长在1 548~1 570 nm内连续可调的短脉冲输出.该激光器可实现自启动锁模,且长时间稳定工作无需任何调整.     

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.     

High-resolution measurement of fiber length by using a mode-locked fiber laser configuration

A simple method to precisely measure fiber length has been experimentally demonstrated by using a mode-locked fiber laser configuration. Since the transit time in a cavity is exactly proportional to the cavity length, it is easy to obtain the fiber length from the generation of mode-locked pulses in the fiber laser with a long-range nonlinear optical loop mirror that includes the measured fiber. Our new method has a large measurement range, over hundreds of kilometers, and a high resolution, of the order of centimeters, as well as no measurement dead zone.     

基于半导体光放大器的非归零信号时钟恢复

提出了一种基于半导体光放大器加窄带光纤光栅滤波器，将非归零信号转换为伪归零信号，再把伪归零信号注入到主动锁模环行腔激光器进行时钟提取的非归零信号时钟恢复方案.利用该方案实现了10 Gb/s伪随机非归零信号的全光时钟恢复，对工作原理和结果进行了分析和讨论.实验证明该方案具有结构简单，调整容易，输出波形好的特点.