掺铒光纤环形激光器中饱和吸收光栅瞬态特性引发跳模的实验研究

在掺铒光纤环形激光器中插入饱和吸收光栅是获得稳定单纵模激光的常用方法,但跳模难以完全避免.通过干涉仪动态相移解调法将光频跳变实时转化为相位变化,发现了一种由饱和吸收动态光栅的瞬态响应特性导致的跳模新机理.实验测量了由腔长快调触发的规则跳模,获得了跳模规律及成因.此种跳模发生在调制曲线斜率最大值附近区域,通常在相邻模式之间出现,跳模前移频量约为纵模间隔.在同等调制振幅下,抽运功率越高,触发跳模所需的光频调制频率越大,所需的最小移频量也越大.实验结果给出了振动和调制条件下激光器稳定工作的条件,这为设计激光器的隔振封装和确定频率调制工作模式下的调制范围提供了实验依据.     

低噪声环形腔掺铒光纤激光器的研究

分析了环形腔掺铒光纤激光器的输出特性,给出了稳态下的激光器输出功率、阈值泵浦功率和斜率效率的解析表达式,为激光器结构的优化提供了依据。搭建了全保偏环形腔掺铒光纤激光器,利用未泵浦铒纤中由驻波干涉和饱和吸收诱发的自写入光纤光栅的窄带滤波特性及反射波长的自适应特性,有效地解决了激光器的跳模问题。通过测量得到激光器系统的泵浦阈值为15.3mW,斜率效率为2.8%,输出偏振度为32dB。利用非平衡光纤干涉仪系统和相位产生载波(PGC)调制解调技术测得激光器的相位噪声为3×10-5rad/Hz~1/2(1kHz)。     

掺铒光纤环形激光器输出特性的研究

根据掺铒光纤激光器的速率方程，对环形腔光纤激光器的输出特性进行了理论分析，得到了光纤激光器在稳态条件下阈值抽运功率、激光输出功率和斜率效率的解析表达式。利用数值模拟结果对光纤激光器的这些基本特性参量进行了分析和讨论，为光纤环形激光器的优化设计提供了依据。并进行了980nm抽运的掺铒光纤激光器的实验，实验证明理论分析得到的基本特性是合理的。     

一种结构新颖的L波段掺铒光纤激光器

提出了一种结构新颖的L波段环形腔掺铒光纤激光器。用掺铒光纤作为增益介,采用980nm激光器作为前向抽运源,利用起偏器和偏振控制器获得L波段激光,利用光环形器将后向的放大自发辐射再引入铒光纤的前端,重复利用。当抽运功率为103mW时得到了阈值功率约为23．87mW,输出功率达6．34mW的激光输出,斜率效率约为8．05％,与没有重复利用后向放大自发辐射谱的掺铒光纤激光器做比较,该结构对L波段掺铒光纤激光器的性能有明显的提升作用。对于长度不合适的铒纤,在没有重复利用后向放大自发辐射谱时没有获得激光输出;而在利用后向放大自发辐射后,在阈值功率约为88mW时得到了激光输出,从而很好地证明了上述结论。     

一种新型自激发布里渊掺铒光纤激光器

利用级联的受激布里渊效应,自激发布里渊掺铒光纤激光器可以实现常温下的多波长激光输出。通过在自激发掺铒光纤激光器中引入一个高双折射萨尼亚克(Sagnac)环形滤波器,调节萨尼亚克环形滤波器的偏振控制器(PC),实现了可调谐多波长输出,同时在实验中观测到双布里渊多波长带的现象。研究了这种光纤激光器中萨尼亚克环形滤波器的带宽和980 nm抽运光功率对输出波长数的影响,在萨尼亚克环形滤波器的带宽为83.3 nm以及980 nm抽运光功率为260 mW时,得到了52个间隔为0.088 nm的多波长激光输出。     

有理数谐波主被动锁模掺铒光纤激光器

在理论上详细分析了利用非线性光学环形镜（NOLM）来减小输出脉冲幅度波动,消除噪声并对脉冲进行压缩整形的物理机制。在主动锁模掺铒光纤环形激光器中（AHML－EDFL）接入一个非线性光学环形镜,形成结构新颖的主被动锁模掺铒光纤激光器（APHML－EDFL）,利用非线性光学环形镜所具有的饱和吸收体功能,成功地制抑了4阶有理数谐波锁模（RHML）中较大的幅度噪声,在1GHz量级的调制频率下,由主被动锁模掺铒光纤激光器获产生重复频率为5．1GHz,幅度相当稳定的4阶有理数谐波锁模脉冲序列。     

损耗调制型掺铒光纤环形激光器混沌现象的实验研究

报道了损耗调制型掺铒光纤环形激光器中的混沌现象.在单频损耗调制型掺铒光纤环形激光器中,改变调制频率或调制电压,观察到倍周期分岔和阵发两种进入混沌途径的共存现象,与抽运调制型掺铒光纤环形激光器的实验结果相一致.提出了一种采用两个正弦信号驱动的损耗调制型掺铒光纤环形激光器,在调制信号频率比近似等于黄金分割数和白银分割数时,增加调制电压,发现激光器通过准周期途径进入混沌.当调制信号两频率比不同时,发生转变所需的调制电压也不同. 关键词： 掺铒光纤环形激光器 混沌 倍周期分岔 准周期     

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.     

Yb∶Er共掺杂对掺铒光纤激光器中自脉冲行为的抑制作用

为了进一步提高镱铒共掺杂光纤激光器的实用性 ,对镱铒掺杂光纤激光器的自脉冲现象进行了理论分析。利用掺杂光纤中铒离子对的可饱和吸收的作用而引起自脉冲运转及离子对互作用模型作为理论基础建立系统模型 ,通过理论计算分析了共掺杂镱后掺铒光纤的有效抽运速率 ,证明了镱铒共掺杂可以提高有效抽运速率。使用这种光纤 ,可以使抑制光纤激光器中离子对导致的自脉冲效应所需的抽运功率水平大大降低。半导体激光器输出的抽运功率足以抑制由离子对导致的自脉冲 ,提供稳定激光运转。在研制稳定单频或高重复频率锁模光纤激光器方面 ,这种可用激光二极管抽运的镱铒共掺光纤具有很大的潜力。     

低阈值展宽脉冲锁模掺Er3+光纤环形激光器的实验研究

将正色散值较小的掺铒光纤引入传统的环形腔构成了低阈值的展宽脉冲锁模激光器.通过使用这种掺铒光纤,激光器的锁模阈值大大降低,激光器的自起振泵浦功率仅为90 mW,而且在29 mW的低泵浦功率时仍然可维持稳定的锁模状态.实验中获得了脉冲宽度为175 fs,光谱半高宽为40 nm,重复频率为33 MHz的锁模脉冲输出.激光器工作稳定,光谱干净光滑.     

Experimental demonstration of novel end-pumping method for double-clad fiber devices

We present experimental demonstration of an end-pumping scheme based on splicing the multimode pump and single-mode signal fibers directly to a double-clad fiber with a tailored cross section. The method is used to pump a double-clad, erbium- and ytterbium-doped, fiber ring laser. The efficiency of the end-pumping method is tested by determining the slope efficiencies of the fiber ring laser and the fiber laser in a Fabry-Perot configuration. Comparable slope efficiencies are found when both laser configurations have similar output coupler ratios. The developed pumping scheme and double-clad fiber can find applications in cost-effective power fiber amplifiers and lasers.     

基于多模光纤滤波器的可调谐掺铒光纤激光器

研究了一种新型、全光纤、宽带可调谐环形腔掺铒光纤激光器。该激光器利用由单模-多模-单模光纤组成的滤波器实现波长可调谐及激光器的全光纤结构。该滤波器将多模光纤缠绕在偏振控制器上,两端分别与一段单模光纤相连,通过调整偏振控制器的状态,实现了中心波长1542～1560nm的不同激光输出。单波长连续可调谐激光器的波长可调范围为18nm,边模抑制比大于40dB,3dB线宽为0.096nm;进一步调整偏振控制器的状态和抽运功率,实验同时得到了连续可调谐的双波长、三波长等多波长激光输出。对于可调谐的多波长激光器,通过调整偏振控制器的状态,可实现波长间隔及输出中心波长两者可调。     

Analysis of laser source nonlinearity due to longitudinal mode-hopping

The nonlinearity of a frequency-ramped single-mode laser source to be used in optical heterodyne interferometry has been investigated. The analysis is based on mode-hopping due to variation in injection current, temperature and mismatch reflections.     

Efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser

A novel approach to achieving robust single-spatial-mode operation of cladding-pumped fiber lasers with multimode cores is reported. The approach is based on the use of a fiber geometry in which the core has a helical trajectory within the inner cladding to suppress laser oscillation on higher-order modes. In a preliminary proof-of-principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 microm diameter core and a numerical aperture of 0.087 has been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M2 < 1.4 for 92.6 W launched pump power from a diode stack at 976 nm. The slope efficiency at pump powers well above threshold was approximately 84%, which compares favorably with the slope efficiencies achievable with conventional straight-core Yb-doped double-clad fiber lasers.     

单模光纤激光极限功率的数值研究

对光纤激光极限功率的探索和其受限因素的分析, 有利于为大功率光纤激光器的发展提供理论依据和实验指导. 本文考虑热效应、光效应、非线性效应和抽运亮度等因素对光纤激光极限功率的影响, 分析了掺镱和掺铥光纤的极限功率和受限因素. 在此基础上, 结合激光在光纤中单模传输的条件, 计算了单模掺镱和掺铥光纤激光的极限功率. 计算结果表明, 在现有技术条件下, 使用常规的976 nm和793 nm激光二极管抽运, 单模掺镱和掺铥光纤激光的极限功率分别为4.2 kW和7.8 kW, 其中单模掺铥光纤激光的功率水平还远低于它的极限功率的原因是受抽运亮度的限制. 最后分析指出减小纤芯的数值孔径和改进少模光束的光束质量是提升单模光纤激光极限功率的重要途径.     

Multi-coupler side-pumped Yb-doped double-clad fiber laser

The side-coupler of angle polished method, using angle-polished multimode fiber and optical adhesive, is used to efficiently pump an Yb-doped double-clad fiber laser. The maximum coupling efficiency of 78.6% is achieved by the side-coupler for a multimode fiber with a circular core of 200 μm and a double-clad fiber with a 350/400 μm D-shaped inner cladding. While laser diodes (LDs) with three side-couplers are simultaneously used as pump sources, maximum output power of 1.38 W and slope efficiency of 48.9% are demonstrated in the fiber laser system.     

High-power continuous-wave cladding-pumped Raman fiber laser

We demonstrate a high-power single-mode cladding-pumped Raman fiber laser. The Raman fiber laser consists of a 1.2 km long germanium-doped double-clad fiber in a linear cavity, which is spliced to a single-mode fiber. The laser is end pumped by a multimode erbium-ytterbium-doped fiber, which is coupled to the inner cladding of the Raman fiber. The embedded core was designed to be single mode at the Raman Stokes wavelength, and up to 10 W of power was obtained at 1660 nm from the single-mode fiber end. The laser has a slope efficiency of 67% and a threshold of 6.5 W.     

Ytterbium-sensitized thulium-doped fiber laser with a single-mode output operating at 1900-nm region

A single-mode laser is demonstrated using a newly developed double-clad thulium-ytterbium-doped fiber (TYDF) in a linear cavity formed by two fiber Bragg gratings (FBGs). The YTF used is drawn from a D-shape preform fabricated using the modified chemical vapor deposition and solution doping technique. The laser is operated at 1 901.6 nm via the transition of thulium ions from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The efficiencies of the laser are 0.71% and 0.75% at 927- and 905-nm multimode pumping, respectively. The thresholds of the launched pump power for 927- and 905-nm pumping are 1 314 and 1 458 mW, respectively. A 7-mW output is obtained at a 905-nm pump power of 2 400 mW.     

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。     

Single-mode Raman fiber laser based on a multimode fiber

Single-mode operation of a Raman fiber laser based on a multimode fiber has been demonstrated for what is to our knowledge the first time. Single-mode operation was achieved through the beam cleanup effect of stimulated Raman scattering in multimode fibers. The Raman laser, consisting of a 50-microm-core multimode fiber and a multimode Nd:YAG laser pump, produced an output beam corresponding to the fundamental mode of the fiber.