Different supercontinuum generation processes in photonic crystal fibers pumped with a 1064-nm picosecond pulse

Picosecond pulse pumped supercontinuum generation in photonic crystal fiber is investigated by performing a series of comparative experiments. The main purpose is to investigate the supercontinuum generation processes excited by a given pump source through the experimental study of some specific fibers. A 20-W all-fiber picosecond master oscillator-power amplifier （MOPA） laser is used to pump three different kinds of photonic crystal fibers for supercontinuum generation. Three diverse supercontinuum formation processes are observed to correspond to photonie crystal fibers with distinct dis- persion properties. The experimental results are consistent with the relevant theoretical results. Based on the above analyses, a watt-level broadband white light supercontinuum source spanning from 500 nm to beyond 1700 nm is demonstrated by using a picosecond fiber laser in combination with the matched photonic crystal fiber. The limitation of the group velocity matching curve of the photonic crystal fiber is also discussed in the paper.     

Supercontinuum generation in seven-core photonic crystal fiber pumped by a broadband picosecond pulsed fiber amplifier

We report a supercontinuum source generated in seven-core photonic crystal fibers(PCFs) pumped by a self-made all-fiber picosecond pulsed broadband fiber amplifier. The amplifier's output average power is 60 W at 1150 nm with spectral width of 260 nm, and its repetition rate is 8.47 MHz with pulse width of 221 ps. With two different lengths of seven-core PCF, different output powers and spectra are obtained. When a 10 m long seven-core PCF is chosen, the output supercontinuum covers the wavelength range from 620 nm to 1700 nm, with the output power of 11.7 W. With only 2 m long seven-core PCF used in the same experiment, the wavelength of the supercontinuum spans from 680 nm to 1700 nm,with the output power of 20.4 W. The results show that the pulse width is 385 ps in the 10 m long seven-core PCF and 255 ps in the 2 m long one, respectively, due to the normal dispersion of the PCF.     

高非线性光子晶体光纤中飞秒脉冲的传输特性和超连续谱产生机制的实验研究及模拟分析

用实验和数值模拟两种方法研究了高非线性光子晶体光纤中飞秒激光脉冲的传输特性和超连续谱的产生机理，给出了抽运脉冲在三种不同中心波长情况下输出光谱展宽并形成超连续谱的实际测量及理论模拟结果.研究表明：在零色散波长抽运时，光谱展宽以自相位调制为主，同时三阶色散的影响明显，传输脉冲在时域内出现振荡次峰.而在反常色散区抽运时，光谱展宽的初期以自相位调制为主，随后根据抽运功率的不同孤子自频移、高阶光孤子的裂变和四波混频效应会逐渐增强，进而成为光谱展宽的主要原因.与此相应，在时域中能明显看到孤子的形成和红移，飞秒传输脉 关键词： 光子晶体光纤 高非线性光子晶体光纤 飞秒脉冲激光 超连续谱     

飞秒激光在光子晶体光纤中产生超连续光谱机制的实验研究

报道了利用零色散在780nm处的光子晶体光纤与纳焦耳量级的飞秒激光脉冲相互作用的实验结果.实验使用35fs，中心波长810—840nm，单脉冲能量可达14nJ的飞秒激光光源获得了超过一个倍频程的平坦超连续光谱（500—1100nm）.在不同功率、不同中心波长、不同啁啾和有无直流成分的多种飞秒脉冲激光的条件下，研究了超连续光谱的产生情况.并对一系列现象进行了对比，分析了超连续光谱产生的机制. 关键词： 光子晶体光纤 飞秒脉冲激光 超连续光谱     

七芯光子晶体光纤中百瓦量级超连续谱的产生

采用平均功率为141.6 W的皮秒光纤激光泵浦一段国产七芯光子晶体光纤,获得了平均功率为104.2 W、连续光谱覆盖范围从750至1700 nm以上的超连续谱输出.详细研究了超连续光谱随泵浦功率增加的演变过程,并对基于该七芯光子晶体光纤的超连续谱光源的光谱拓展和功率提升潜力进行相关的分析和讨论.该研究结果对高功率超连续谱光源的发展具有一定的参考价值.     

光子晶体光纤超连续谱产生的实验研究

报道了利用掺钛蓝宝石飞秒激光器产生重复频率为80MHz,脉宽为10fs的超短激光脉冲在10cm长光子晶体光纤产生超连续谱的实验,获得展宽范围为450nm到1100nm的连续谱。实验中观察到孤子自频移和高阶孤子分裂现象,非孤子辐射与随后光谱向短波方向的拓展有密切关系。     

基于光子晶体光纤的百瓦量级超连续谱光源研究

采用脉冲重复频率可调的高功率皮秒脉冲光纤激 光抽运光子晶体光纤产生了平均输出功率为101 W的全 光纤化超连续谱. 通过一系列的对比实验, 详细研究了抽运激光的脉冲重复频率以及光子晶体光纤的长度对超连续谱产生的影响. 最后, 对如何实现更高平均功率的超连续谱输出进行相关的分析和讨论. 相关研究结果可以为进一步发展基于光子晶体光纤的高功率超连续谱光源提供一定的参考. 关键词： 光子晶体光纤 非线性光纤光学 超连续谱产生     

光子晶体光纤超连续谱产生过程中色散波的孤子俘获研究

基于光子晶体光纤中脉冲演化遵循的非线性薛定谔方程, 用数值模拟的方法分别研究了飞秒脉冲在单零色散点和双零色散点光子晶体光纤中超连续谱的产生和色散波的孤子俘获现象. 结果表明: 与单零色散点光子晶体光纤相比, 双零色散点光子晶体光纤产生的超连续谱既包含了蓝移色散波, 又包含了红移色散波, 且当满足群速度匹配时, 孤子通过四波混频不仅能俘获蓝移色散波, 而且能俘获红移色散波, 从而产生新的俘获波频谱成分. 为了清楚地观察脉冲传输的时频特性, 通过模拟交叉相关频率分辨光学开关技术, 得到了孤子俘获色散波的演化过程. 关键词： 超连续谱 色散波 孤子俘获 光子晶体光纤     

Recent developments in high power near-infrared super-continuum generation based on photonic crystal fiber

High power supercontinuum generation has witnessed rapid developments during the past few years. The mechanism and the latest achievements in high power supercontinuum generation are reviewed both for the continuous wave pump regime and the pulsed pump regime. The challenges in scaling the average power of supercontinuum generation are analyzed. Some of our works on high power supercontinuum generation are summarized, and perspectives for the future development are discussed.     

Visible supercontinuum generation in tapered photonic crystal fiber pumped by picosecond pulse at 1064 nm

Short photonic crystal fibers (PCFs) with different tapered waist diameter are made to extend the continuum spectrum in the visible range. The diversification of output continuum spectrum with the diameter of the tapered waist is experimentally observed. An all fiber visible supercontinuum source with 1.88 W output is demonstrated in our experiments. To the best of our knowledge, it is the highest all fiber visible supercontinuum generation in tapered PCF, pumping by picosecond pulse at 1064 nm. The suitably designed short tapered PCF can extend the visible spectrum, while, how to preserve the tapered waist is crucial for the all fiber visible supercontinuum source in the practical applications.     

飞秒激光脉冲在高非线性光子晶体光纤中产生超连续谱的实验研究

使用钛宝石激光器抽运一根长1m的高非线性光子晶体光纤,获得的超连续谱波长覆盖范围为420—1700nm,输出功率为170mW,转换效率在20%以上;对实验结果给出了详细的分析,并与理论模拟结果相比较,认为超连续谱产生的主要原因是高阶孤子的分裂和四波混频效应.同时研究了不同抽运功率和不同抽运波长下超连续谱产生的情况,发现对同一根光纤,抽运功率由小到大变化时,可将输出的光谱分为初始展宽,剧烈展宽和饱和展宽三个阶段,当输出的光谱处于初始展宽和饱和展宽阶段时,都会存在一定的抽运残留,当输出的光谱处于剧烈展宽时,转 关键词： 光子晶体光纤 超连续谱 高阶孤子 反常色散区     

飞秒光脉冲在光子晶体光纤中的非线性传输和超连续谱产生

采用分步傅里叶方法数值模拟了飞秒光脉冲在光子晶体光纤中非线性传输和超连续谱的产生. 计算和分析了高阶色散和非线性效应对超连续谱形状和带宽的影响. 结果表明在光子晶体光纤中产生了孤子自频移现象. 同时也发现脉冲内拉曼散射和自相位调制的联合作用导致了超连续谱中精细结构的出现. 另外，还发现高阶色散和初始光脉冲的峰值功率对超连续谱的带宽和平滑也有直接影响. 关键词： 光子晶体光纤 孤子自频移 超连续谱     

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber（PCF） is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power（i.e.,37 mW）,which indicates that the polarization state is well maintained.     

High stability supercontinuum generation in lead silicate SF57 photonic crystal fibers

We report supercontinuum (SC) generation in a lead silicate SF57 photonic crystal fiber by using a 1550 nm pump source. The effective nonlinear coefficient of the SF57 fiber is simulated to be 111.5 W-1 ·km-1 at 1550 nm. The fiber also shows ultraflat dispersion from 1700 nm to 2100 nm. Our results reveal that with an increase of the average power of the incident pulse from 10 mW to 90 mW, the SC of the SF57 photonic crystal fiber is generated from 1300 nm to 1900 nm with high stability and without significant change in spectral broadening.     

Mid-infrared supercontinuum and optical frequency comb generations in a multimode tellurite photonic crystal fiber

We numerically investigate the mid-infrared(MIR) supercontinuum(SC) and SC-based optical frequency comb(OFC) generations when the three optical modes(LP01, LP02, and LP12) are considered in a multimode tellurite photonic crystal fiber(MM-TPCF). The geometrical parameters of the MM-TPCF are optimized to support the multimode propagation and obtain the desired dispersion characteristics of the considered three optical modes. When the pump pulse with center wavelength λ = 2.5 μm, width T = 80 fs, and peak power P = 18 k W is coupled into the anomalous dispersion region of the LP01, LP02, and LP12 modes of the MM-TPCF, the-40-d B bandwidth of the generated MIR SCs can be up to2.56, 1.39, and 1.12 octaves, respectively, along with good coherence. Moreover, the nonlinear dynamics of the generated SCs are analyzed. Finally, the MIR SCs-based OFCs are demonstrated when a train of 50 pulses at 1-GHz repetition rate is used as the pump source and launched into the MM-TPCF.     

Generation of mid-infrared supercontinuum by designing circular photonic crystal fiber

A circular photonic crystal fiber (C-PCF) based on As₂Se₃ is designed, which has three zero dispersion wavelengths and flat dispersion. Using this fiber, a wide mid-infrared supercontinuum (MIR-SC) can be generated by launching a femtosecond pulse in the first anomalous dispersion region. The simulation results show that the MIR-SC is formed by soliton self-frequency shift and direct soliton spectrum tunneling on the long wavelength side and self-phase modulation, soliton fission on the short wavelength side. Further, optical shocking and four-wave mixing (FWM) are not conducive to the long-wavelength extension of MIR-SC, while the number and intensity of fundamental solitons have a greater effect on the short-wavelength extension of MIR-SC. The generation of optical shocking waves, FWM waves and fundamental solitons can be obviously affected by changing the fiber length and input pulse parameters, so that the spectrum range and flatness can be adjusted with great freedom. Finally, under the conditions of 4000 W pulse peak power, 30 fs pulse width, 47 mm fiber length, and 0 initial chirp, a wide MIR-SC with a coverage range of 2.535 μm-16.6 μm is obtained. These numerical results are encouraging because they demonstrate that the spread of MIR-SC towards the red and blue ends can be manipulated by choosing the appropriate incident pulse and designing optimized fiber parameters, which contributes to applications in such diverse areas as spectroscopy, metrology and tomography.     

孤子光脉冲的产生及其应用研究

利用非线性偏振旋转技术实现自起振被动锁模.在掺铒光纤环形腔激光器中产生了中心波长为1563.3 nm、重复频率为12.5 MHz、脉冲宽度为352.0 fs、3 dB光谱宽度为7.8 nm的孤子光脉冲.采用该孤子光脉冲作为抽运光源，经掺铒光纤放大器放大后，输入到101 m长的高非线性光子晶体光纤中，获得了20 dB带宽约为240 nm的超连续激光光谱.实验详细观测了光脉冲随抽运功率的变化及超连续激光光谱的形成过程，分析了其形成机理.研究表明：当抽运功率较低时，光谱加宽主要由高阶孤子的分裂引起；随着抽运功率的增加，高阶孤子分裂成基本孤子的数目逐渐增大，光谱进一步加宽；当抽运功率增加到受激拉曼散射的阈值时，受激拉曼散射成为光谱展宽的主要原因；抽运功率进一步增加时，受激拉曼散射、参量四波混频等非线性的共同作用将使光谱进一步加宽且变得光滑. 关键词： 孤子光纤激光器 超连续 光子晶体光纤     

全波段正常色散光子晶体光纤中超连续谱的产生

设计了一种铅硅酸盐SF57 材料的光子晶体光纤, 利用有限元法数值模拟了该光纤的 色散特性. 研究结果显示在整个透明波段光纤具有正常色散. 利用自适应分布傅里叶法求解非线性薛定谔方程, 对中心波长为1550 nm, 初始脉宽为150 fs 的脉冲在该光纤中传输进行了模拟, 获得了关于入射脉冲中心波长对称的展宽范围超过了600 nm 的超平坦连续光谱, 并且光谱具有极其稳定和 相干的特性. 关键词： 光子晶体光纤 超连续谱产生 正常色散     

Fiber optical parametric oscillator based on photonic crystal fiber pumped with all-normal-dispersion mode-locked Yb:fiber laser

We demonstrate a cost effective, linearly tunable fiber optical parametric oscillator based on a home-made photonic crystal fiber pumped with a mode-locked ytterbium-doped fiber laser, providing linely tuning ranges from 1018 nm to 1038 nm for the idler wavelength and from 1097 nm to 1117 nm for the signal wavelength by tuning the pump wavelength and the cavity length. In order to obtain the desired fiber with a zero dispersion wavelength around 1060 rim, eight sam- ples of photonic crystal fibers with gradually changed structural parameters are fabricated for the reason that it is difficult to accurately customize the structural dimensions during fabrication. We verify the usability of the fabricated fiber experimen- tally via optical parametric generation and conclude a successful procedure of design, fabirication, and verification. A seed source of home-made all-normal-dispersion mode-locked ytterbium-doped fiber laser with 38.57 ps pulsewidth around the 1064 nm wavelength is used to pump the fiber optical parametric oscillator. The wide picosecond pulse pump laser enables a larger walk-off tolerance between the pump light and the oscillating light as well as a longer photonic crystal fiber of 20 m superior to the femtosecond pulse lasers, resulting in a larger parametric amplification and a lower threshold pump power of 15.8 dBm of the fiber optical parametric oscillator.     

基于低非线性系数光子晶体光纤的全光纤高效超连续谱光源

报道了一种基于低非线性系数光子晶体光纤的全光纤高效率超连续谱产生系统。将光纤锁模激光器输出的脉宽5 ps、重复频率20 MHz、平均功率50 mW的脉冲,输入到15 μm的大模场光纤中进行放大,通过与两级芯径较小的短光纤模场匹配缩小输出的模场直径后,输入到20 m低非线性系数的光子晶体光纤,获得的超连续谱波长覆盖范围宽于650～1 700 nm。输入光子晶体光纤的泵浦光功率为740 mW,输出超连续光功率为670 mW,转换效率大于90%。实验研究了超连续光谱展宽的过程,从理论上进行了分析解释。