微纳光纤及其锁模激光应用

微纳光纤是一种直径接近或小于传输光波长的纤维波导,由于纤芯和包层折射率差较大,具有强光场约束、强倏逝场、低损耗、反常波导色散、表面均匀性好和机械性能高等特性。近年来,以纳米材料作为饱和吸收体的被动锁模激光器成为超短脉冲激光技术方向的研究热点。得益于微纳光纤的强光场约束能力及大比例倏逝场,纳米材料与微纳光纤的复合结构能显著增强光与物质的相互作用,进而降低该复合结构的饱和吸收阈值,为超短脉冲产生和非线性动力学等研究提供一个新颖而灵活的平台。同时,微纳光纤因具有反常波导色散、光谱滤波、饱和吸收和偏振敏感等特性,在激光器的色散调控、偏振锁模等方面获得应用。介绍了微纳光纤的制备和特性以及在锁模激光方面的典型应用和相关技术的最新进展,并就未来的发展方向进行了展望。     

NbSe2纳米颗粒锁模的2μm光纤激光器

高重频大脉冲能量激光在基础科学研究以及通信、探测、材料加工等应用领域具有重要价值。报道了溶液法制备的过渡金属二硫化物NbSe2纳米颗粒材料的线性和非线性光学特性,并利用其2μm波段可饱和吸收特性对掺铥光纤激光器进行被动调制实现了2μm锁模激光输出。线性测量发现NbSe2纳米材料的光学吸收覆盖近红外到近中红外波段且随波长增加而降低;非线性光学测量显示NbSe2纳米材料在2μm波段的调制深度为6.5%、饱和强度为19 MW·cm^−2。然后我们把NbSe2纳米材料转移到金镜上制作成可饱和吸收器件,并对掺铥光纤激光器进行调制得到2μm耗散孤子谐波锁模激光,单脉冲能量为3.36 nJ,脉冲宽度为1.48 ns,重复频率为50.66 MHz。激光光谱的中心波长为1910.8 nm,光谱宽度为5.8 nm。首次在2μm光纤激光器中采用NbSe2纳米颗粒实现耗散孤子锁模,证明了NbSe2纳米材料在2μm波段的非线性光学调制能力,结合纳米颗粒的可集成特性,溶液法制备的NbSe2纳米材料有望成为一种新型的宽谱非线性光电调制材料/器件。     

基于纯水可饱和吸收体的1.9μm波段被动调Q和锁模掺铥光纤激光器

构建了纯水作为可饱和吸收体的被动调Q和锁模掺铥光纤激光器.通过陶瓷套管将纯水固定在两个光纤跳线头之间,调整水层厚度可以分别实现调Q和锁模操作.调Q状态下的最大输出功率为0.531 mW,此时的重复频率为53.45 kHz,脉冲宽度为3.01μs.锁模状态下的最大输出功率为2.28 mW,重复频率为17.69 MHz,脉冲宽度为1.42 ps.本文使用纯水作为可饱和吸收体的被动锁模光纤激光器,其具有皮秒级的响应时间、低廉的价格和极高的损伤阈值,可为掺铥全光纤脉冲激光器提供一种新方案.     

基于金属/介质混合反射镜的高调制深度半导体可饱和吸收镜锁模的飞秒光纤激光器

介绍了一种新型半导体可饱和吸收镜(SESAM)的原理与特性,并用它来实现掺铒光纤激光器的锁模飞秒脉冲的生成.这种新型宽带SESAM调制深度可以达到20%,用在1.5μm波段的环形腔掺铒光纤激光器里,实现自启动锁模.锁模光谱以1559 nm为中心,半峰全宽为9 nm,锁模激光脉冲串重复频率为25.6 MHz,输出功率14 mW,自相关仪测得脉宽为170 fs.     

快速与慢速饱和吸收体被动锁模掺铒光纤激光器的理论分析

利用半导体饱和吸收波导作为慢速饱和吸收体与非线性快速饱和吸收体相结合，建立了共同被动锁模掺铒光纤激光器的理论模型-分析了半导体饱和吸收波导、光纤自相位调制和自振幅调制对锁模脉冲宽度和脉冲啁啾的影响- 关键词：     

自调Q自锁模固体激光器

利用被动锁模激光器的锁模原理,结合自锁模固体激光器中等效快可饱和吸收体的特性,讨论了控制运转状态的自锁模动力学方程和速率方程,给出了自调Q自锁模的条件,以及自调Q周期与激光器结构和运转参数的关系,所得结论与实验结果有很好的一致性。     

自调Q、自锁模铒/镱共掺光纤激光器

研究了结构新颖的环形腔铒/镱（Er/Yb）共掺双包层光纤激光器.为了获得高功率激光输出,使用6个激光二极管（LD）同时抽运Er/Yb共掺光纤,采用光纤光栅（FBG）Sagnac环作为波长选择器,得到了中心波长为1548.11 nm、谱线宽度为0.06 nm的窄线宽激光输出;并利用增益光纤作为可饱和吸收体,实现了自调Q、自锁模脉冲输出.当抽运功率为719 mW时,激光器输出自调Q脉冲,脉冲周期为20μs,脉冲宽度为2.8μs,脉冲的平均功率为38.4mW,峰值功率为274.3mW;当抽运功率为3.6 W时,激光器输出自锁模脉冲,脉冲宽度为4ns,平均功率为319 mW,脉冲峰值功率大于10 W,重复频率为7.937 MHz.     

10kHz腔倒空锁模皮秒激光器研究

将半导体可饱和吸收体(SESAM)锁模技术与腔倒空技术结合,采用半导体端面抽运方式实现了具有高重复频率、大单脉冲能量的皮秒激光器的运转.从理论上分析了腔倒空锁模输出的机理,建立起腔倒空锁模激光器运行的物理图像,并对影响激光器倒空率的一些因素进行了研究.实验上,实现端面抽运Nd:YVO4晶体的SESAM连续锁模后,在锁模...     

2 μm波段全光纤保偏被动锁模掺铥光纤激光器

报道了2 m波段的全光纤保偏锁模掺铥光纤激光器,通过在法布里-珀罗（F-P）腔内加入半导体可饱和吸收镜做为被动锁模器件,采用主振-放大构型,获得了最高输出平均功率为1.08 W,重复频率为10.24 MHz,脉冲宽度为15.24 ps,中心波长为2054.68 nm,光谱宽度约为0.3 nm的2 m线偏振激光脉冲输出,激光脉冲的消光比为24.17 dB。     

2μm波段全光纤保偏被动锁模掺铥光纤激光器

报道了2μm波段的全光纤保偏锁模掺铥光纤激光器,通过在法布里-珀罗(F-P)腔内加入半导体可饱和吸收镜做为被动锁模器件,采用主振-放大构型,获得了最高输出平均功率为1.08W,重复频率为10.24MHz,脉冲宽度为15.24ps,中心波长为2054.68nm,光谱宽度约为0.3nm的2μm线偏振激光脉冲输出,激光脉冲的消光比为24.17dB。     

All-fiber mode-locked fiber laser

An environmentally stable mode-locked fiber laser based on nonlinear polarization rotation is experimentally demonstrated. The laser is based on a novel laser configuration that has negligible low-power steady-state reflectivity from one side and, consequently, no CW gain. The laser is self starting and the configuration is implementable as an all-fiber laser with standard polarization-maintaining fiber-pigtailed components. A pulse duration of 5.6 ps is obtained at a repetition rate of 5.96 MHz and at an average power of 8 mW. As an application of the proposed laser configuration, 213 mW of supercontinuum (600-1750 nm) was demonstrated from a fiber laser system with no sections of free-space optics.     

All-fiber bidirectional passively mode-locked ring laser

We report the design and operation of a novel all-fiber bidirectional passively mode-locked ring laser. An erbium-doped fiber was chosen as the active element in a ring cavity arrangement. A short segment of a fiber taper embedded in carbon nanotubes/polymer composite, acting as a saturable absorber, was used to enable bidirectional mode locking. The laser generates two stable femtosecond pulse trains in opposite directions. A beat note of about 2 MHz, having a bandwidth of less than 2 kHz, is measured when the pulses propagating in opposite directions are (temporally) overlapped at a photodetector. We believe this device will find important applications in precision rotation sensing.     

All-fiber normal-dispersion mode-locked laser with gain filter

An all-fiber normal-dispersion mode locked laser is presented. No additional spectral filter components are involved in the cavity. Spectral filtering is achieved through gain narrowing by three segments of gain fibers with different lengths. The performances of the fiber lasers with and without gain narrowing are discussed. A stable mode locked pulse train is observed in the cavity with gain filtering with pulse duration of 72 ps. The gain filtering effect is discussed theoretically.     

All-fiber wavelength tunable passively mode-locked erbium-doped ring laser

An all-fiber, wavelength-tunable, passively mode-locked erbium-doped ring laser is presented. Erbium-doped fibers (EDF) are used as the gain media because of their large gain bandwidth. Nonlinear polarization rotation (NPR) plays the dual role of realizing mode-locking and effectively adjusting the intensity-dependent loss of the cavity. An unbalanced Mach-Zehnder interferometer (UMZI) is used as a tunable optical beam filter. By using the UMZI and adjusting the polarization controllers (PCs), a sub-picosecond mode-locking laser is realized that is self-starting with central lasing wavelengths that can be accurately tuned over a range of about ~ \sim 30 nm and also has controllable spacings between different tunable wavelengths.     

All-fiber add-drop filters based on microfiber knot resonators

We demonstrate an all-fiber add-drop filter composed of a microfiber knot (working as a resonator) and a fiber taper (working as a dropping fiber). The dropping taper can be either parallel or perpendicular to the input port of the filter. A quality factor (Q factor) of 13,000 is obtained from a parallel-coupling 308 microm diameter microknot add-drop filter with a free spectral range (FSR) of 1.8 nm. A Q factor of approximately 3300 is obtained from a cross-coupling 65 microm diameter microknot add-drop filter with a FSR of 8.1 nm. This device is particularly easy to fabricate and to connect to fiber systems.     

All-fiber passive mode-locked laser to generate ps pulses based in a symmetrical NOLM

We experimentally investigate an all-fiber passively mode-locked laser generating ps pulses. The experimental setup is a figure eight fiber laser configuration, including a power-symmetric Nonlinear Optical Loop Mirror (NOLM) with highly twisted low-birefringence fiber in the loop. NOLM switching is achieved by polarization asymmetry between the counter-propagating beams in the loop. We used a Quarter-Wave Retarder in the loop to break the polarization symmetry. Using a polarizer beam-splitter cube as the NOLM output we got the best quality output pulses from the laser. At this output, we are monitoring the output pulse polarization component which is parallel to the input NOLM component. We achieved stable generation of ～25 ps pulses at the repetition frequency of 0.78 MHz with milliwatts average output power. The mode-locked laser ran in stable operation for hours.     

All-fiber polarization locked vector soliton laser using carbon nanotubes

We report an all-fiber mode-locked erbium-doped fiber laser (EDFL) employing carbon nanotube (CNT) polymer composite film. By using only standard telecom grade components, without any complex polarization control elements in the laser cavity, we have demonstrated polarization locked vector solitons generation with duration of ~583 fs, average power of ~3 mW (pulse energy of 118 pJ) at the repetition rate of ~25.7 MHz.     

All-fiber passively mode-locked laser oscillator at 1.5 microm with watts-level average output power and high repetition rate

We report on a passively mode-locked all-fiber laser oscillator at 1.5 microm based on heavily doped phosphate-glass active fiber. An active fiber only 20 cm long is sufficient to produce as much as 2.4 W of average output power directly from the oscillator. The width of the mode-locked pulses varies from 8 ps at the lowest output power in the mode-locked state to 44 ps at the highest power. Our picosecond laser oscillator features a high repetition rate of 95 MHz and high peak pulse power of approximately 540 W. The oscillator combines the convenience of all-fiber construction with power performance that was previously achievable only with mode-locked bulk-optic laser oscillators or more complex systems involving fiber amplifiers.     

Actively mode-locked fiber laser using a deformable micromirror

We present what we believe to be the first fiber laser system that is actively mode-locked by a deformable micromirror. The micromirror device is placed within the laser cavity and performs a dual function of modulator and end-cavity mirror. The mode-locked laser provides ~1-ns-long pulses with 20 nJ/pulse energy at 5 MHz repetition rates.     

All-fiber actively Q-switched Yb-doped laser

An all-fiber actively Q-switched Yb-doped laser is presented. Q-switching is performed by modulating a fiber Bragg grating via a magnetostrictive rod which is fixed to the fiber at the position of the grating. By exposing the rod to a changing magnetic field, the rod is stretched and relaxed causing the Bragg wavelength of the grating to shift and thereby changes the Q-factor of the cavity. Using Yb-doped fiber, pulses at 1052 nm are obtained at repetition rates from 1 to 200 kHz. At 75 kHz, 0.5 μJ pulses with peak powers of 3 W can be produced when 180 mW of pump power is applied. To the knowledge of the authors, this is the first all-fiber actively Q-switched Yb-doped laser presented to date.