光学微腔中倍频光场演化和光谱特性

在考虑光学微腔中二阶和三阶非线性效应的情况下,引入了可同时描述腔内基频和倍频光场的演化过程的Lugiato-Lefeve方程,分析了SiN微腔中二次谐波的产生,并讨论了各参数对腔内基频和倍频光场的影响.理论分析结果表明,失谐参量为0时,稳定后的基频光场为平顶脉冲的形式,而倍频光场呈正弦分布;失谐参量增加,将导致腔内基频和倍频光功率在演化过程中出现振荡,且最终稳定的光功率变弱,稳定后的光场分布为周期性变化;失谐参量的值过大,会使得微腔光场处于混沌状态.抽运光强较弱时,腔内可形成稳定的光场分布;抽运光强较强时,会导致腔内色散以及非线性效应过强,最终稳定的光场仍然呈周期性变化,且抽运光功率越强,光功率的演化曲线振荡越强.此外,选取特定的微腔尺寸,微腔可工作于"图灵环"状态.理论分析结果对研究光学微腔中二次谐波的产生有重要意义.     

一种基于非线性光纤环镜开关特性的超短光孤子产生方法

提出了一种利用非线性光纤环镜的开关特性将连续波同时转化为亮孤子和暗孤子的新方法 ,即让连续波和另一波长的调制脉冲串共同耦合入光纤环镜 ,交叉相位调制使得一部分连续波被环镜透射 ,其余部分被反射 ;再让透射波和反射波分别在反常色散光纤和正常色散光纤中传输 ,自相位调制和群速度色散之间的相互作用使得透射波和反射波分别演化为亮、暗孤子。数值计算表明 ,该方法不仅可产生脉宽比调制脉冲窄、重复频率比调制脉冲高的亮孤子和暗孤子 ,而且几乎可将全部的连续波能量转化为孤子能量。     

光纤中基于互相位调制效应的超短光脉冲对的产生

提出一种在单模光纤正常色散区由连续波产生超短光脉冲对的新方法.即让连续波和一个波长位于光纤负色散区的高阶孤子在光纤中同时传输,互相位调制效应和群速度色散效应的互相作用能使连续波演化成超短光脉冲对.本文还通过计算机模拟,对该方法进行了全面的考察和分析.结果表明,此方法实用且效果较好.     

Efficiency of frequency-pulsed excitation of a micron-sized spherical microcavity by chirped ultrashort laser radiation

Peculiarities of internal optical field resonant excitation inside micron-sized spherical transparent dielectric cavity illuminated by a train of ultrashort laser pulses are investigated. On an example of water microdroplet is shown that optimal tuning of incident radiation to a selected high-Q resonance electromagnetic cavity mode can be realized by varying temporal interpulse interval in a laser train together with linear frequency modulation of every pulse (chirp). Efficiency of resonant particle excitation by a chirped picosecond pulses train can be considerably increased as compared to unchirped pulse train and CW excitation also.     

Sub-100 kHz repetition rate erbium-doped fiber laser in anomalous dispersion regime

We propose and demonstrate a simple but efficient way to generate low repetition rate pulses in an erbium-doped fiber ring laser by using self-pulsing technique. About 2.25 km long single mode fiber is used to elongate in the cavity, providing large anomalous cavity dispersion in the wavelength region around 1550 nm. Self pulses at a repetition rate of 85.3 kHz with single pulse energy as high as 110 nJ are efficiently obtained on the nanosecond time scale. The experimental results demonstrate that the self-pulse fiber laser operating in the anomalous dispersion regime can also realize high-energy pulses at a very low pulse repetition rate.     

Soliton formation with controllable frequency line spacing using dual pumps in a microresonator

Temporal cavity solitons(CSs) have excellent properties that can sustain their shape in a temporal profile and with a broadband, smooth-frequency spectrum. We propose a method for controllable frequency line spacing soliton formation in a microresonator using two continuous-wave(CW) pumps with multi-free-spectral-range(FSR) spacing. The method we propose has better control over the amount and location of the solitons traveling in the cavity compared to the tuning pump method. We also find that by introducing a second pump with frequency N FSR from the first pump, solitons with N FSR comb spacing can be generated.     

End-pumped all solid-state high repetition rate Tm,Ho:LuLF laser

The characteristics of diode end-pumped Tm,Ho:LuLiF for continuous wave (CW) running and high pulse repetition frequency (PRF) Q-switched operation are illustrated. In the CW mode, 950-mW output power with a slope efficiency of 24% is obtained. In the Q-switched mode, output energy of 78 μJ under 10 kHz with a slope efficiency of 23% is achieved. The pulse stability, pulse width as a function of pump intensity, and spectral characteristics are also analyzed.     

High-repetition-rate Nd:YVO4 slab laser with a 1-D top-hat output beam

A high-repetition-rate electro-optic Q-switched Nd:YVO₄ slab laser is demonstrated in this paper. The Nd:YVO₄ slab inside the compact resonator is end-pumped by a 2-bar laser diode stack. The output beam with one dimension (1-D) top-hat intensity distribution at both near field and far field is generated. Continuous wave (CW) output of 13 5 W is obtained under the total pump power of 50 W. At the repetition rate of 40 kHz, the energy per pulse is 0.32 mJ with its pulse width of 26.3 ns. At 20 kHz, we have achieved the maximum pulse energy of 0.56 mJ and 56 kW peak power with 10 ns pulse width.     

Second-harmonic generation taking into account dispersion of nonlinear susceptibility

Second-harmonic generation in the field of an ultrashort pulse and the propagation of extremely short pulses in a medium with quadratic nonlinearity are analyzed. Second-harmonic generation is analyzed taking into account the effect of second-and third-order group velocity dispersion and dispersion of nonlinear susceptibility up to the second order. Corrections, whose order of smallness is determined by the parameter (ω_L t _p)^?1, where t _p is the pulse duration and ω_L is the carrier frequency of the pump wave, are obtained. For a large phase mismatch, two new solutions are found that describe the stationary evolution of solitary pump and second-harmonic waves in the regions of both anomalous and normal group velocity dispersions.     

Harmonic Mode-Locked Ytterbium-Doped Fibre Ring Laser

We demonstrate a harmonic mode-locked ytterbium-doped fibre ring laser, which consists of a polarization-sensitive isolator, two polarization controllers, two 976nm laser diodes as the pump source and a two-segment ytterbium-doped fibre. Utilizing an additive pulse mode-locked technique based on nonlinear polarization evolution, the ytterbium-doped fibre laser can operate in mode-locked state by adjusting the position of polarization controllers. The cavity fundamental repetition rate is 23.78 MHz. We also observe the second- and third-harmonic mode locking in the normal dispersion region, and their repetition rates are 47.66 MHz and 71.56 MHz, respectively. Over-driving of the saturable absorber in the harmonic mode-locking pulse is analysed and discussed in detail.     

Q-switched operation of an in-band-pumped Ho:LuAG laser with kilohertz pulse repetition frequency

We report continuous-wave (CW) and repetitively Q-switched operation of an in-band-pumped Ho:LuAG laser at room temperature. End-pumped by a Tm:YLF solid-state laser with emission wavelength of 1.91 μm, the CW Ho:LuAG laser generated 5.4-W output at 2100.7 nm with beam quality factor of M ²～1.03 for an incident pump power of 14.1 W, corresponding to slope efficiency of 67% with respect to absorbed pump power. Up to 1.5-mJ energy per pulse at pulse repetition frequency (PRF) of 3 kHz and 4.5-W average power with FWHM pulse width of 28 ns at 5 kHz were demonstrated in repetitively Q-switched operation.     

Efficient continuous wave and Q-switched operation of a dual-end-pumped <Emphasis Type="Italic">c</Emphasis>-cut Tm:YAP laser

An efficient continuous wave (CW) and Q-switched c-cut Tm:YAP laser is reported in this letter. With the dual-end-pumped convex-concave resonator, CW output power up to 13.6 W at 1.99 μm was obtained under a total incident pump power of 50 W. The corresponding slope efficiency was 34.3% and conversion efficiency was 27.2%. The active Q-switched operation of the laser had an average output power of 12.5 W at 10 kHz pulse repetition frequency, with a minimum pulse width of 126 ns. With 6 kHz pulse repetition frequency, the maximum pulse energy of 1.6 mJ was obtained. In addition, using the Tm:YAP laser as a pumping source for gain-switched Cr:ZnSe laser, as much as 4 W output power in the wavelength range of 2.5–2.6 μm was obtained.     

Generation of 10-GHz ultra-short pulses with low time jitter in an actively mode-locked fiber laser

We have experimentally achieved the 8.3-ps ultra-short pulse at 10 GHz repetition rate with the time jitter as low as 590 fs in an actively mode-locked fiber ring laser. The ring-cavity laser is mode-locked by a semiconductor optical amplifier based on cross-gain modulation. The external CW source is modulated with radio frequency signal by an amplitude modulator as the external optical pulses and, then, injected into the fiber ring cavity to achieve active mode locking. Further investigating the laser output characteristics, it indicates that the linewidth of employed CW source affects properties of the generated ultra-short pulse, such as phase noise and time jitter. Ultra-short pulse at high repetition rate with low time jitter can be generated by the optimization of CW laser source.     

单模光纤中基于交叉相位调制的压缩脉冲对产生

基于波长位于反常色散区强泵浦脉冲的交叉相位调制,通过对波长位于正常色散区的弱脉冲在单模光纤中的传输进行数值模拟,得出了一种压缩脉冲的新方法.计算结果表明,在零色散波长位于弱脉冲波长和泵浦脉冲波长中间附近的情况下,交叉相位调制(XPM)与群速度色散(GVD)的共同作用能使弱脉冲演化成比其初始宽度窄得多的脉冲对.同时我们还发现,泵浦脉冲的相对于信号脉冲初始峰值功率愈高,初始相对宽度越小,所得弱脉冲的压缩比和压缩后脉冲峰值功率愈高,压缩到最窄时所需光纤长度越短.最后对基于这一压缩的物理机制作了详尽的分析.     

Dynamics of the spectral width of intense laser pulses consisting of several field oscillations in optical waveguides

The dependence of the rms spectral width of a light pulse consisting of several light-field oscillations on the distance passed in an optical waveguide with arbitrary dispersion and nonresonant electronic nonlinearity has been derived. This dependence allows one to rapidly predict the scenarios of the initial evolution of the spectrum (broadening, distance independence, or compression) by using the input pulse parameters and waveguide characteristics. It is shown that the pulse spectral width increases when the enrichment of the spectrum due to the generation of multiple harmonics is taken into account. In this case, for pulses with the spectrum in the region of the anomalous group dispersion of the waveguide, there is the intensity range for which the self-narrowing of the main spectral peak around the central radiation frequency is characteristic.     

Passive Q-switching of Pulsed and CW Nd: YAG Lasers with Cr~(4 ): YAG

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光纤中基于拉曼放大与脉冲压缩的超短光孤子产生

提出一种在单模光纤负群速色散枢由弱脉冲产生高强度超短光孤子的新方法。     

基于石墨烯的1 064 nm连续锁模超短脉冲激光器

介绍了利用沉积在增透镜上的石墨烯薄膜作为可饱和吸收体、808 nm激光二极管端面泵浦Nd∶YVO4晶体的1 064 nm连续锁模激光输出特性。采用W型折叠谐振腔结构,在808 nm泵浦功率为8.0 W时,有稳定的连续锁模脉冲输出,平均输出功率达到185 mW;当抽运功率增加到16.0 W时,获得了中心波长1 063.4 nm、脉冲宽度为518 fs、重复频率为66.7 MHz、最大平均输出功率为323 mW的百飞秒量级超短脉冲激光输出。实验结果表明:石墨烯具有优良的可饱和吸收性,在1 064 nm波段能够实现高功率、百飞秒量级连续锁模脉冲激光输出。     

Performance of actively Q-switched Nd:LiLuF<Subscript>4</Subscript> crystal end-pumped by a 792 nm laser diode

An efficient laser diode end-pumped continuous-wave (CW) and AO Q-switched laser of Nd:LiLuF₄ crystal with dual central wavelengths of 1053.1 and 1054.7 nm is reported for the first time. The maximum CW output power of 6.22 W was obtained at absorbed pump power of ∼14.6 W with the output transmission of 2%. The optical conversion efficiency is ∼43%, corresponding to a slope efficiency of about 48% with respect to the absorbed pump. For the Q-switched operation, the shortest pulse width of 17 ns was obtained at the pulse repetition frequency (PRF) of 0.5 kHz, resulting in a pulse energy of 2.24 mJ and peak power of 131.8 kW.     

Simultaneous wavelength tuning and amplitude modulation in QPM optical parametric amplifiers

We repot simultaneous optical parametric amplifiers (OPA) and amplitude modulation of signal pulse in a monolithic periodically poled KTP (PPKTP) by electrically controlling the relative phase between the pump, signal and idler waves in a KTP dispersion section sandwiched between two PPKTP gratings, theoretically. The controlling electric field can be arbitrary direction. For an ultrashort pulse group velocity mismatch, group dispersion and diffraction must be regarded, simultaneously. The solutions of the truncated equations, including the above effects in the two PPKTP gratings of simultaneous frequency tuning and amplitude modulation OPA, were analyzed. It is shown that the intensity of output signal pulse of OPA depends on the thickness of the dispersion section, the magnitude and azimuth of controlling electric field and one evidences periodicity. For the certain angular dispersion there exist the largest frequency bandwidths of optical parametric amplifiers. Certain angular dispersion of a signal pulse can increase the frequency bandwidth, and broadband amplification of ultrashort pulse can be performed effectively.