连续波锁模掺钕磷酸盐玻璃激光器光学谐振腔的分析

由于Nd:磷酸盐玻璃的热导率和破坏阀值都比较低,故连续波锈模钕磷酸盐玻璃激光器要求其谐振腔有特殊的设计.本文在谐振腔长度固定的限制下,分析了三元件式谐振腔的特性,并且讨论了连续波主动锁模Nd:磷酸盐玻璃激光器光学谐振腔的设计.我们讨论了在不同参量范围下谐振腔的稳定性范围和特性,并且阐明了有关的最佳参数的范围.给出了谐振腔最佳运转区参数的解析表达式.实验结果与理论预测符合得很好.这个解析式对设计三元件或多元件的任何端面泵浦和锁模谐振腔是很有用的.     

An Experimental Study on the Output Properties of an Actively Mode-locked Er~(3 ) Doped Fiber Ring Laser

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Lyot filter based multiwavelength fiber ring laser actively mode-locked at 10 GHz using an electroabsorption modulator

A multiwavelength fiber ring laser comprising of a Lyot filter and hybrid gain medium is presented. A wavelength channel spacing of 100 GHz is achieved by appropriate tuning of the Lyot filter length. Four wavelength channels are simultaneously mode-locked at 10 GHz using an electroabsorption modulator. We highlight how the intra-cavity modulator can affect the stability of the mode-locked laser spectrum when used in conjunction with a Lyot filter. We show that, due its reduced polarization sensitivity, an electroabsorption modulator significantly improves the stability of the mode-locked laser spectrum when compared to using a Mach-Zehnder modulator.     

Timing and detuning studies of a synchronously pumped mode-locked dye laser

The timing relationship between a synchronously pumped mode-locked dye laser and its pump laser is explored experimentally and theoretically. The experimental data is in quantitative agreement with numerical solutions of a semiclassical model that includes no free parameters. The data also agrees qualitatively with an approximate, analytic distillation of this model which is presented here for the first time. Our study has a direct bearing on the jitter and the long term stability of these important ultrashort pulse lasers.     

高稳定性、高质量脉冲压缩飞秒光纤激光系统研究

报道了一款用于眼科手术的高稳定性、高质量脉冲压缩飞秒光纤主振荡功率放大系统. 振荡器采用混合腔方式增加了光纤双折射, 改善了非线性偏振旋转锁模在低重复频率下无法自启动的缺点, 提高了飞秒光纤激光器自启动锁模的稳定性. 研究了脉冲预啁啾与飞秒脉冲压缩质量的关系, 通过实验证明了光纤放大器的入射脉冲保持负的预啁啾状态可以得到最好的脉冲压缩结果. 实验最终实现了满足自启动锁模条件的重复频率19.4 MHz、平均功率1.2 W、脉冲宽度183 fs的激光脉冲, 目前这台激光器是国内首台具有自主知识产权并应用于动物角膜实验的飞秒光纤激光器.     

Frequency offset locking of a synchronously pumped mode-locked dye laser

We have developed a scheme of frequency offset locking for transferring the frequency stability of a commercial dye laser to a synchronously pumped mode-locked dye laser. By observing the beat frequency between the two dye lasers, mode stability of less than 2 MHz has been observed for the mode-locked dye laser mode. The use of the mode-locked system as a spectroscopic tool has been demonstrated by observing Doppler-free multiple pulse two photon spectra of the sodium 3S-4D transition.     

Generation of wideband tunable femtosecond laser based on nonlinear propagation of power-scaled mode-locked femtosecond laser pulses in photonic crystal fiber

We implement an experimental study for the generation of wideband tunable femtosecond laser with a home-made power-scaled mode-locked fiber oscillator as the pump source.By coupling the sub-100 fs mode-locked pulses into a nonlinear photonic crystal fiber(NL-PCF),the exited spectra have significant nonlinear broadening and cover a spectra range of hundreds of nm.In experiment,by reasonably optimizing the structure parameters of NL-PCF and regulating the power of the incident pulses,femtosecond laser with tuning range of 900-1290 nm is realized.The research approach promotes the development of femtosecond lasers with center wavelengths out of the traditional laser gain media toward the direction of simplicity and ease of implementation.     

Different operation states of soliton pulses in an erbium-doped fibre ring laser

We report on the experimental observation of soliton pulses in an erbium doped fibre ring laser. The passive mode-locking is achieved using the nonlinear polarization rotation technique. By adjusting the pump power and the intracavity polarization controllers, a normal soliton, a stable 8th harmonic mode-locked pulse and a noise-like pulse have been observed in our laser. The experimental results revealed that the noise-like pulse is not suitable for the optical telecommunication, and in order to obtain the stable harmonic mode-locked soliton, a strong unstable CW laser field is necessary to mediate global soliton interaction. The formation mechanism of the harmonic mode-locked pulse has also been analysed.     

High-stability passively mode-locked laser based on dual SESAM

A novel passively continuous-wave mode-locked laser by using two semiconductor saturable absorber mirrors (SESAMs) was demonstrated. The obtained average output power was 2.4 W with a pulse width of 9.97 ps and a pulse repetition rate of 127 MHz. The dual-SESAM mode-locked laser operation was more stable than the cases with single SESAM. The experimental results show that the long-term stability of the dual-SESAM mode-locked picosecond lasers provides promising potential for industrial applications.     

56 MHz重复频率端泵SESAM连续波锁模Nd∶YVO4激光器

为了增大皮秒注入种子激光的能量,获得较高的激光放大效率和信噪比,关键是要在保持较高的平均锁模激光功率下实现连续波锁模激光器的低重复频率运转。通过选取五镜折叠激光谐振腔腔型和参数设计,克服了随着腔长增加损耗加大而导致的激光锁模不稳定的困难。分析了较长腔长条件下工作物质和SESAM光斑尺寸的大小和变化,及其对激光器稳定性的影响。由于SESAM饱和工作和稳态条件的能量要求,在激光谐振腔调整过程中,对应臂长的光程互补变化。实验中采取腔长和晶体热控制方式,优化了激光谐振腔的工作参数,实现了脉冲能量10.7 nJ,重复频率56 MHz,平均功率1.2 W的SESAM连续波锁模激光输出。     

Experimental and theoretical studies of a high repetition rate fiber laser, mode-locked by external optical modulation

An experimental and theoretical study of a high repetition rate laser source operating on a novel mode-locking technique is presented. This technique relies on the fast saturation and recovery of a semiconductor optical amplifier induced by an external optical pulse and has been used to obtain 4.3 ps pulses at 20 GHz. A complete mathematical model of the fiber ring laser is presented describing the mode-locking process in the laser oscillator and providing solutions for the steady-state mode-locked pulse profile. The critical parameters of the system are defined and analyzed and their impact on the formation of the mode-locked pulses is examined. The comparison between the theoretical results and the experimental data reveals very good agreement and has allowed the optimization of the performance of the system in terms of its critical parameters.     

Diode array pumped, non-linear mirror Q-switched and mode-locked Nd : YVO4 laser — a good tool for powder SHG measurement

A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO₄ laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser while operating in QML regime is much higher but pulses suffers from poor amplitude stability. The incorporation of an acousto-optic modulator as an active Q-switch enhances the stability of the QML pulse envelope. The second-order non-linearity of powdered crystalline urea is conclusively measured with respect to KDP while the laser is operating in passively Q-switched and passively mode-locked regime as well as in actively Q-switched and passively mode-locked regime.     

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。     

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.     

Diode end-pumped self-Q-switched and mode-locked Nd,Cr：YAG /KTP green laser

We first experimentally demonstrate a laser-diode end-pumped self-Q-switched and mode-locked Nd,Cr:YAG green laser with a KTP crystal as the intra-cavity frequency doubler. The device produces an average output power of 680 mW at 532 nm. The corresponding pulse width of the Q-switched envelope of the green laser is 170±20 ns. The mode-locked pulses have a repetition rate of approximately 183 MHz and the average pulse duration is estimated to be around sub-nanosecond. It is found that the intra-cavity frequency doubling greatly improves the modulation depth and stability of the mode-locked pulses within the Q-switched envelope.     

Period-doubling of gain-guided solitons in fiber lasers of large net normal dispersion

We report on the experimental observation and numerical simulations of period-doubling of gain-guided solitons in an erbium-doped fiber laser operating in the large net normal cavity dispersion regime. Features of the solitons before and after the period-doubling bifurcation are studied. Our results suggest again that period-doubling is an intrinsic feature of the mode-locked soliton lasers, which is independent of the mode-locked pulse property.     

Generation of bound solitons in actively phase modulation mode-locked fiber ring resonators

Bound solitons generated in actively mode-locked lasers enable new forms of pulse pairs and multiple pairs or groups of solitons in optical transmission or logics. In this paper, we present the generation of stable bound states of multiple solitons in an active mode-locked fiber laser using continuous phase modulation for wideband phase matching. Not only that dual-soliton bound states but also the triple- and quadruple-soliton pulses can be established. Simulation of the generated solitons are demonstrated. We have also prove by simulation that experimental relative phase difference and chirping caused by phase modulation of LiNbO₃ modulator in the fiber loop significantly influences the interaction between the solitons and hence their stability as they circulate in the anomalous path-averaged dispersion fiber loop.     

Investigation of the parameters of a high-power picosecond feedback controlled chirp pulsed amplified Nd: glass laser with injection seeding

We describe experimental studies to investigate the parameters of a compact high-power Nd: glass laser. The laser consists of a mode-locked oscillator with negative feedback (=1.4ps), a Q-switched pre-amplifier with an amplification factor of 5×10⁸, and multiple stage amplifiers using a chirped pulse amplification compression technique.     

利用啁啾脉冲光谱滤波和非线性偏振旋转技术实现高稳定性和开机自启动的全光纤掺Yb~(3+)光纤锁模激光器

建立理论模型,讨论了非线性偏振旋转全光纤锁模激光器的锁模过程、谐波过程以及导致激光器锁模运行难以稳定的影响因素.讨论了采用啁啾脉冲光谱滤波产生脉冲自振幅调制、增加激光器锁模稳定性和自启动能力的机理以及非线性偏振旋转与啁啾脉冲光谱滤波相结合实现锁模的物理过程和脉冲演化过程.研制出全光纤结构的超短脉冲掺Yb~(3+)光纤环形激光器,采用非线性偏振旋转和啁啾脉冲光谱滤波相结合的锁模技术,实现了激光器锁模的开机自启动和高稳定运行.对激光器进行了长期运行稳定性、锁模开机自启动能力、锁模输出参数可重复性监测.锁模脉冲中心波长1052.9 nm,谱宽9.1 nm,脉冲能量4.25 nJ,脉冲宽度17.8 ps.运行期间,各参数波动均小于0.3%.开机自启动能力和可重复性测试显示,激光器可实现一键自启动,启动后各参数可重复精度在0.55%以内.     

Regeneratively mode-locked fiber laser with a repetition rate stability of 4.9x10-15 using a hydrogen maser phase-locked loop

We demonstrate an ultrastable regeneratively mode-locked fiber laser that employs a phase-locked loop (PLL) circuit with a hydrogen maser. The stability for an integration time of 1s was 6.2x10(-13), which is 16 times better than that of a conventional PLL laser. For an integration time of 1000s, the stability reached as high as 4.9x10(-15). The repetition-rate stability was limited by the synthesizer used for the PLL operation, and there was no additional fluctuation induced by the laser operation.