利用半导体可饱和吸收镜实现的全光纤被动锁模激光器

设计了包含半导体可饱和吸收镜(SESAM)、单包层高掺Yb增益光纤和光纤布拉格光栅(FBG)的全光纤激光器,实现了皮秒级,中心波长约为1064 nm,3 dB线宽约为0.4 nm,重复频率约为17.3 MHz的稳定的连续(CW)被动锁模脉冲输出。观察并分析了输出激光随抽运功率升高和降低的变化过程,升高过程中连续锁模启动时抽运功率阈值为50 mW,降低过程中能够实现稳定锁模的最小抽运功率为37 mW。随着抽运功率的加大,首先出现调Q现象。然后出现连续锁模,并伴有很小幅度的调Q现象。继续加大功率,脉冲会出现分裂;抽运功率越大,单脉冲分裂成的多脉冲越多,多脉冲调制越强。在较少脉冲演变为较多脉冲的过程中,会出现调制的不稳定性。当抽运功率足够大时.会出现多脉冲个数及峰值的不稳定现象。半导体可饱和吸收镜被动锁模会使输出激光谱线加宽,随着抽运功率的加大和锁模的加强,输出激光谱线逐渐加宽。随着脉冲分裂个数增多,单个脉冲脉宽变窄。在多脉冲调制阶段,外界微扰会对系统产生一定影响。     

A low-threshold efficient KTA OPO by a fiber-coupled diode-end-pumped Nd:YVO4 laser

A low-threshold efficient high-repetition-rate eye-safe optical parametric oscillator(OPO) is presented.The OPO is based on an x-cut non-critically phase-matched(NCPM) KTA intra-cavity pumped by an acousto-optically(A-O) Q-switched Nd:YVO4 laser.At 10 kHz,the lowest threshold of 0.75 W and the signal power of 0.6 W are got,corresponding to the single pulse energy of 60 μJ and the peak power of 20 kW.Tuning the frequency,the maximum output power at 1536 nm is 1.03 W at 30 kHz with an optical-to-optical conve...     

Diode-pumped actively Q-switched Nd： YAG laser at 946 nm

A diode-pumped Nd： YAG acousto-optically（A-O） Q-switched laser at wavelength 946 nm formed with a simple plane-plane cavity has been demonstrated. The maximum average output power was 850 mW. The highest peak power was 531 W with the pulse repetition rate of 20 kHz and pulse width of 80 ns at the incident pump power of 19.5 W.     

Widely and continuously tunable optical parametric generator based on MgO-doped periodically poled LiNbO3 crystal

Pulsed optical parametric generators(OPGs)and op-tical parametric oscillators(OPOs)have beenextensive-ly studied and developedfor generatingtunable coherentsources[1-5]that cover the wide spectral range fromthenear UVto the mid IR.In this letter we report…     

Actively $Q$ -switched and Mode-Locked Diode-Pumped ${hbox {Nd:GdVO}}_{4}{hbox {--KTP}}$ Laser

By using a comparative simple configuration and a short cavity length, a diode-pumped actively Q -switched and mode-locked intracavity frequency doubled Nd:GdVO₄-KTP green laser with the modulation depth 100% was realized, from which the great average output power, the high efficiency were obtained and the mode-locked pulse inside the Q -switched pulse has a repetition rate of 476 MHz. Using the hyperbolic secant function methods and by considering the Gaussian distribution of the intracavity photon density, the influences of continuous pump rate, the upper state lifetime of the active medium and the turnoff time of the acousto-optic Q -switch, we proposed a developed rate equation model for actively Q -switched and mode-locked green lasers. With this developed model, the theoretical calculations are in good agreement with the experimental results and the width of the mode-locked green pulse is estimated to be about 185 ps.     

光子晶体光纤中基于交叉相位调制的脉冲压缩

为了研究飞秒双脉冲在光子晶体光纤不同色散区的非线性传输过程,采用分步傅里叶方法求解耦合的非线性薜定谔方程组,并进行了理论分析。讨论了不同抽运功率、不同抽运脉冲啁啾参量以及不同脉宽比对信号脉冲压缩的影响。结果表明,基于交叉相位调制效应,弱信号脉冲不仅能够被压缩,而且光纤存在最佳压缩长度。增大抽运脉冲输入功率,选取正啁啾抽运脉冲,可以得到更大的信号脉冲压缩因子,同时最佳光纤长度减小。另外,不同的脉冲宽度对信号脉冲的压缩产生大的影响,较窄脉宽的抽运脉冲易于产生较短的压缩信号脉冲。这一结果对用光子晶体光纤压缩弱信号脉冲提供了理论参考。     

The power spectrum of digital FM as produced by digital circuits

A simple exact method is given for calculating the power spectrum of a frequency modulated filtered M-ary data signal. The power spectrum and its discrete components are given in closed form for any pulse shape. The pulses are those generated by a digital transversal filter and the FM modulator is that composed of an ideal digital integrator followed by a phase modulator (look-up table).     

Experimental investigation on evolution of a split multi-wavelength bright-dark pulse in a mode-locked thulium-doped fiber laser

We report the experimental observation of evolving phenomenon of a split multi-wavelength bright-dark pulse in the nonlinear amplifying loop mirror (NALM)-based mode-locked thulium-doped fiber laser (TDFL) with a figure-eight configuration. Bright-dark pulse with 10 wavelengths was successfully obtained at the pump power of 3 W. The time interval between the bright and dark pulses was discovered not only increasing linearly with the pump power but also approximately equaling to the reciprocal of modulation frequency of radio frequency (RF) spectrum. Moreover, we also observed that the spectrum of split multi-wavelength bright-dark pulse can further present up to 13 wavelengths.     

利用SBS调Q的喇曼频移Nd:YAG激光器研究

对采用SBS调Q产生喇曼频移输出的激光器进行了理论分析,并对实验结果与染料调Q时的输出进行了对比,提出了改进该种激光器性能的方法。     

Ytterbium-doped fiber ring laser in multi-pulse operation

An Ytterbium-doped mode-locked fiber laser using the polarization sensitive isolator and polarization controllers (PC) is reported. In the normal dispersion, the fiber laser can oscillate at the multi-pulse states by adjusting the position of the PC. On the condition that the polarization state isn’t changed, the outputs of Ytterbium-doped mode-locked fiber laser change from single pulse to multi-pulse by increasing the pump power. The fiber laser can achieve different multi-pulse output by adjusting the PC1 and PC2 carefully.     

FM and AM mode locking of the homogeneous laser--Part I: Theory

A new general analysis for mode-locked operation of a homogeneously broadened laser with either internal phase (FM) or amplitude (AM) modulation is presented in this paper. In this analysis, a complex Gaussian pulse is followed through one pass around the laser cavity. Approximations are made to the line shape and modulation characteristics to keep the pulse Gaussian. After one round trip, a self-consistent solution is required. This yields simple analytic expressions for the pulse length, frequency chirp, and bandwidth of the mode-locked pulses. The analysis is further extended to include effects of detuning of the modulator, in which case analytical expressions are obtained for the phase shift of the pulse within the modulation cycle, the shift of the pulse spectrum off line center, the change in pulse length, and the change in power output. Numerical results for a typical Nd:YAG laser are given. In the case of the FM mode-locked laser it is found that there is a frequency chirp on the pulse and that this causes pulse compression and stretching when the modulator is detuned. Etalon effects and dispersion effects are also considered.     

2.5 GHz and 5 GHz harmonic mode-locking of a diode-pumped bulkerbium-ytterbium glass laser at 1.5 microns

Third-order harmonic mode locking of a diode-laser pumped bulk Er:Yb:glass laser by frequency modulation with a lithium niobate modulator is reported. Stable pulses at a repetition rate of 2.5 and 5 GHz with a pulse duration down to 9.6 ps are obtained. The average output power is 3 mW, the pulse peak power is 120 mW at 2.5 GHz repetition rate, and the pulses are approximately 1.4 times transform limited. The pulse duration can be increased up to 30 ps by decreasing the mode-locker drive power     

基于交叉相位调制的孤子脉冲压缩效应研究

在负色散区 ,基本孤子在光纤中传输时其波形与脉宽保持不变。提出一种在负色散区利用交叉相位调制效应压缩基本孤子脉冲的新方法。采用分步傅里叶方法对非线性耦合方程进行了数值计算与模拟。研究了不同抽运功率、不同抽运脉冲啁啾参数以及不同脉宽对基本孤子脉冲压缩的影响。发现基本孤子脉冲不仅能够被压缩 ,而且光纤存在最佳压缩长度。在抽运功率一定的条件下 ,选取负啁啾的抽运脉冲 ,可获得更高压缩比的压缩光脉冲。另外 ,不同的脉冲宽度对孤子脉冲的压缩产生较大的影响 ,一般情况下 ,选用较窄的抽运脉冲易于产生较短的压缩光脉冲     

High power output quasi-continuous-wave nanosecond optical parametric generator based on periodically poled lithium niobate

We report on a high power output quasi-continuous-wave nanosecond optical parametric generator （OPG） of congruent periodically poled lithium niobate （PPLN） pumped by a 1 064 nm acousto-optically Q-switched Nd-YVO4 laser （duration. 70 ns,repetition rate：45 kHz,spatial beam quality M2〈 1,3）. The OPG consists of a 38.7 mm long PPLN crystal with a domain period of 28.93 μm. With 5.43 W of average pump power the maximum average output power is 991 mW at 1 517.1 nm signal wave of the PPLN OPG.     

基于高Q值Si3N4片上光学微腔的孤子光频梳

高Q值片上微腔已被证明是一种性能优异的克尔孤子光学频率梳产生平台。由片上多模波导构成的Si₃N₄微腔可以同时实现产生暗孤子所必须的高品质因子和反常色散。为了进一步降低产生单孤子光频梳的阈值功率,文章设计了一种具有欧拉弯曲的新型跑道型Si₃N₄微腔,与传统的圆形弯曲波导相比,跑道型微腔直波导连接处弯曲半径的突然变化被显著抑制,这抑制了高阶模式耦合并降低了传播损耗,从而获得了超过5×10⁶的品质因子。基于该新型微腔,使用辅助激光加热方法仅用47mW泵浦激光器(估计片上泵浦功率为33mW)就产生了重复频率在Ka波段且带宽超过20nm(对应于129fs的脉冲持续时间)的单孤子微腔光频梳。     

光纤中基于交叉相位调制与喇曼放大的超短光脉冲串的产生

本文提出一种在单模光纤负群速色散区连续波产生超短光脉冲串的新方法，即让波长位于光纤负色散区的连续波和波长位于光纤正色散工铁泵浦脉冲串在光纤中共同传输，在光纤的零色散波位于连续波长与泵浦脉冲波长中间附近的情况下，交叉相位调制与喇曼放大能使连续波演化成比泵浦脉冲窄得多的无调啾，无脉座的超短光脉冲串。数值计算表明，泵浦脉冲愈强，由连续波产生的超短光脉冲宽度愈宽，峰值功率愈高，而且所需的光纤愈短。     

调Q及连续掺Yb光纤激光器中的自锁模研究

在用半导体激光器抽运的单包层掺Yb调Q光纤激光器中观察到了清晰稳定的自锁模脉冲序列。脉冲包络形状为调Q脉冲。每个锁模脉冲的幅值由其在调Q脉冲中的相应位置决定。经过分析，认为自相位调制是调Q光纤激光器中产生锁模的主要原因。自相位调制的存在使得光脉冲的频谱被展宽，当这种展宽和腔的模式间隔相差不多时，腔内的模式便能相互作用，直到它们之间产生一个固定的相位关系。也即形成锁模。在此基础上。去掉声光晶体，并用两个光栅作为腔镜，实现了全光纤法布里-珀罗(F-P)腔锁模光纤激光器。改变腔结构，分别采用光栅和光纤反射圈作为前后腔镜，同样观察到了锁模脉冲。经过观察发现，锁模脉冲的产生和掺Yb光纤的浓度、长度、抽运功率的大小有着密切的关系。这为锁模脉冲的产生提供了一种新的方法。     

全光纤电光主动调Q激光器

利用马赫曾德尔Mach-Zehnder (M-Z)结构的尾纤型铌酸锂(LiNbO3)电光强度调制器作为Q开关元件,采用974nm半导体激光器作为泵浦源,峰值吸收系数为110dB/m的掺杂铒纤作为增益介质,实现了1550nm波长的全光纤主动调Q激光器。通过电光强度调制器对腔内损耗进行周期性调制,实现Q开关作用,获得了稳定的调Q脉冲输出。实验中通过改变泵浦功率和调制频率,研究了脉冲宽度和峰值功率的变化规律。获得输出脉冲重复频率50Hz-88kHz可调,重复频率1kHz时获得最窄脉冲宽度246ns,峰值功率近5W。     

Development of a new adaptive sigma-delta modulator scheme applied to multilevel inverter control

Interest in multilevel inverters is increasing in recent years, especially in high voltage applications. Traditional pulse width modulation (PWM) techniques can be applied to control this type of switched converter. However, it is necessary to adapt these techniques to the particularities of multilevel operation. As an alternative, other modulation techniques, such as sigma-delta modulation (SDM) can be used. In this case, it is possible to use advanced modulation techniques, such as adaptive modulation, to adapt the SDM to the multilevel operation. This article presents a new adaptive sigma-delta modulator that controls a five levels multilevel inverter. The algorithm that generates the sigma-delta signal is implemented in a field-programmable gate array (FPGA). This allows a very fast operation independent of the overall control circuit operation response. In addition, the FPGA can generate the control signals necessary to drive the power semiconductors in the power stage. The resulting modulator is simpler than the PWM version.     

基于相位调制和光参量放大的光短脉冲源实验研究

提出了一种基于光参量放大和相位调制加色散压窄产生高消光比短脉冲源的新方法.连续抽运光首先经过LiNbO<,3>强度调制器,利用强度调制的倍频调制特性产生占空比为33%的光脉冲,再经相位调制器在脉冲的主体部分引入最大线性正啁啾,经参量放大后所生成的闲频光的啁啾为抽运光的2倍,通过合适的色散介质得到了11.4 ps的短脉冲...