基于倍频波长转换中走离效应产生多个脉冲的研究

利用倍频光与泵浦光脉冲之间的走离效应,通过在周期性极化的LiNbO3波导中间增加两段未被极化的波导,1.55 μm波段的泵浦脉冲在极化的波导部分产生0.77 μm波段的倍频光,在未被极化的部分不产生倍频光,形成了三个被间隔开来的倍频子脉冲.通过差频将三个倍频子脉冲还原成1.55 μm波段的三个差频脉冲,实现了用一个泵浦脉冲产生三个转换脉冲.用数值模拟计算展示脉冲的产生及其演化过程,并讨论了用LiNbO3波导参量控制脉冲特征参量的方法.     

周期极化铌酸锂波长转换器脉冲抽运时的波形畸变

理论分析了周期性结构的LiNbO3晶体(PPLN)光波导在脉冲光抽运时的级联二阶非线性效应,并通过数值计算得到了抽运、倍频、信号及转换四个光脉冲的波形在波导中的演化。研究表明,使用脉冲光抽运时,由于抽运光脉冲与倍频光脉冲之间的群速度失配导致的走离,将使倍频光脉冲产生展宽;再通过差频转换使得转换光脉冲产生了波形畸变和峰值偏移。最后通过实验验证了转换光脉冲的波形畸变。     

脉冲泵浦波长转换改善泵浦带宽容限的研究

基于准相位匹配铌酸锂波导的波长转换,分析了采用脉冲泵浦的方法提高泵浦带宽容限的机理.研究表明:窄脉冲的频带内包含有大量的频谱分量,这些谱分量可以通过倍频效应和和频效应两种机制产生0.8 μm波段的光场,使泵浦带宽容限得到了改善.理论计算和实验都证明了在40G Hz 的ps级脉冲泵浦的波长转换时,－3 dB泵浦带宽容限提高到大约3 nm.     

逆向注入波长转换方式对转换光脉冲畸变的改善

数值模拟分析了在周期域反转结构的铌酸锂光波导中的脉冲抽运波长转换过程,通过对转换过程中光脉冲波形的演化分析,讨论了抽运光和信号光同向和逆向两种注入方式对转换光脉冲波形的影响.研究结果表明在同向注入方式下由于倍频与差频效应是同时进行的,群速度失配导致的走离效应使倍频光脉冲在波导内不断展宽,遗传给差频转换时,使转换光脉冲发生了波形畸变;为防止转换脉冲发生畸变,提出了采用单片光波导用抽运光和信号光逆向注入的方式,将倍频与差频效应分开来,二次非线性效应不再同时进行,从而改善了转换光脉冲的波形畸变,同时提高了转换效率.     

基于PPLN波导中倍频与差频效应的全光波长转换

对准相位匹配的铌酸锂光波导中基于倍频与差频级联二阶非线性效应的全光波长转换进行了研究.在建立理论模型的基础上,分别对单脉冲以及序列光脉冲的波长转换过程进行了数值模拟,并对转换过程中的走离现象以及脉冲延迟进行了分析.模拟结果表明信号光与抽运光脉冲非同步输入的情况下可以克服走离效应的影响,得到更好的转换效率.另外,在抽运时钟脉冲的驱动下,输入的40 Gb/s的NRZ信号光可以转换为RZ转换光,且波形较好.     

周期极化LiNbO3脉冲走离效应分析

 建立了包含高阶群速色散的OPCPA 数值模拟程序，并以准相位匹配的周期极化的LiNbO₃(PPLN)参量放大器为例，在信号光是中心波长1 053 nm，脉宽100 fs的飞秒脉冲经展宽器展宽800 ps的啁啾脉冲，输入能量约0.6 nJ，泵浦光波长527 nm，脉宽3 ns，初始输入泵浦光强300 MW/cmLiNbO²，PPLN晶体的非共线角1.49°，极化周期9.7 μm的条件下， 对OPCPA过程前级的高阶群速色散引起的走离效应对泵浦光、信号光频谱和脉冲形状的影响等具体特性进行了数值模拟。结果表明：在合适的晶体长度下，高阶群速色散对参量转换效率的影响不大，但它对输出信号光的时间波形和频谱有较大影响，会引起脉冲时间形状畸变和频谱漂移。     

单到单和单到双信道皮秒脉冲全光波长转换的实验研究

基于周期极化反转铌酸锂（PPLN）光波导级联倍频和差频（SHG+DFG）的二阶非线性效应,提出并实验研究了皮秒脉冲的可调谐波长转换以及单信道到双信道的波长转换.信号光采用重复频率为40 GHz,脉宽为1.57 ps的脉冲信号.连续抽运光由光纤环形腔激光器（FRL）提供.不同于传统的SHG+DFG型波长转换,信号光固定在PPLN光波导倍频过程的准相位匹配（QPM）波长处,通过调节抽运光的波长实现了转换空闲光的可调谐输出.当使用两个抽运光时实验观察到了单信道到双信道的波长转换.     

新型双环腔结构可调谐全光波长转换器的实验研究

利用周期性畴反转铌酸锂光波导级联和频与差频的二阶非线性效应，提出并实验验证了一种新颖的基于无源光波导双环腔结构的可调谐全光波长转换方案，实现了皮秒脉冲从信号光波长到空闲光波长的转换.采取的脉冲信号光脉宽为1.57ps，重复频率为40GHz，抽运光和控制光由双环腔激光器提供，无需任何外界注入连续光. 关键词： 全光波长转换器 双环腔 周期性畴反转铌酸锂 级联和频与差频二阶非线性效应     

三硼酸锂晶体Ⅰ类非临界相位匹配下近红外波段的差频产生

利用差频发生器产生波长范围为1.1~2.2μm的可调谐近红外激光.实验搭建了差频光路系统,以0.56~0.71μm染料激光器作为泵浦光、1.064μm的半导体激光器作为信号光,经过三硼酸锂晶体在Ⅰ类相位匹配方式条件下通过温度调谐非临界相位匹配方式差频产生较高功率的近红外激光,在近红外波段测得其平均输出功率在30mW以上.泵浦光功率为1.2 W、信号光功率为0.31 W时,测得差频波长为1.54μm的输出功率为35mW,转化效率达11.7%.该近红外差频发生器具有宽调谐、窄线宽的特点.     

周期域反转铌酸锂可调谐波长转换器的皮秒脉冲实验

实验研究了周期域反转铌酸锂光波导级联和频与差频二阶非线性效应(cSFG/DFG)皮秒脉冲间的可调谐波长转换。信号光采用重复频率为40 GHz,脉宽为1.57 ps的脉冲信号。当输入信号光和第一个控制光波长分别为1554.4 nm和1532.5 nm时,通过调节第二个控制光波长由1550.5 nm到1541.0 nm,输出信号光波长可从1536.0 nm调谐至1545.2 nm。当输入信号光波长改变时,通过改变第一个控制光波长以满足和频过程的准相位匹配条件,同时调节第二个控制光波长可以实现输出信号光波长的可调谐。实验中利用两个窄带可调谐滤波器有效抑制了掺铒光纤放大器引入的放大自发辐射噪声,同时观察到了波长下转换和波长上转换。     

Difference-Frequency Generation Among Ultrashort Optical Pulses in Quasi-Phase-Matching Waveguides

A theoretical model of ultrashort pulse difference-frequency generation (DFG) is presented and developed with quasi-phase matching (QPM) gratings in the undepleted-pump, unamplified-signal approximation. An analytic solution to a case of ultrashort pulse pumped DFG process, including group-velocity mismatching effects and input pulses with frequency chirp and time delay, is obtained. The influences of group-velocity mismatching effects and input signal pulse parameters on the conversion efficiency and output converted pulse characteristics are analyzed and discussed. The results indicate that the conversion efficiency is increased due to the enhancement of pump and signal interaction. The output pulse is inevitable compressed under pulsed pumping and can be compensated by introducing the initial frequency chirp and time delay.     

Reduction of light signal pulse distortion in cascaded sum-frequency-generation and difference-frequency-generation wavelength conversion

Cascaded sum-frequency-generation (SFG) and difference-frequency-generation (DFG) can implement a wavelength conversion between arbitrary combinations of input and output signal wavelengths. By using a tunable wavelength pump light, the output wavelength can be tuned to a desired wavelength. As in many wavelength conversion devices using the nonlinear optical effect, the group velocity difference between light pulses with different wavelength causes a walk-off effect deforming the output pulse shape. Thus the device length should be kept short to avoid the walk-off effect resulting in limited conversion efficiency. In this report, we propose a method for a quasi-phase matched (QPM) device to maintain the pulse shape of the SFG light pulse along the propagation distance. The output DFG light pulse deformation is suppressed and the conversion efficiency can be increased by extending the device length.     

Optimization of the idler wavelength tunable cascaded optical parametric oscillator based on chirp-assisted aperiodically poled lithium niobate crystal

We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators(OPO) in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous difference frequency generation(DFG) process by monolithic aperiodically poled, magnesium oxide doped lithium niobate(APMg LN) crystals. The APMg LN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMg LN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal working conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 μJ and 700 μJ are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMg LN crystal is optimized according to this pump condition. To the best of our knowledge,this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMg LN crystals.     

Femtosecond pulse generation using stimulated Raman scattering in integrated silicon optical waveguide device

To generate ultrafast femtosecond optical pulses, we propose a model of an integrated device consisting of a Mach-Zehnder interferometer (MZI) with two symmetric 3 dB directional couplers and a straight waveguide based on the single-mode silicon-on-insulator (SOI) optical waveguide. The principle of pulse generation in the presented device is based on the strong stimulated Raman scattering (SRS) in silicon; the center wavelength of the pulse generated is tunable by changing the center wavelength of the co-propagating pump pulse. Numerical results show that, when a continuous wave (CW) with a weak power at 1670 nm wavelength and a pump pulse with a high peak power at 1550 nm wavelength are co-propagating, a narrow femtosecond pulse with a pulse width (full width at half maximum, FWHM) of ∼60 fs (FWHM of the pump pulse is 166.5 fs) can be achieved in the device proposed. In addition, when the waveguide length, pump peak power, and pump-pulse width are fixed, the properties of generated femtosecond pulse depend strongly on the incident chirp of the pump pulse and the CW power.     

双波长双脉冲激光三次谐波的产生方法

提出双波长双脉冲激光产生三次谐波的方法。波长不同的两脉冲激光束由反射使它们合拢后通过两块非线性的BBO晶体 ,激光脉冲第一次通过BBO晶体产生两波长的二次谐波 (SHG) ,它们由各自的反射镜反射再次通过BBO又产生了二次谐波 ,这两次产生的二次谐波和基波通过用于产生三次谐波的BBO晶体可产生双波长的三次谐波 ,它们由 45°斜置的耦合镜输出。文中分析了满足二次谐波和三次谐波的四个相位匹配的条件 ,该方法也可用于腔内双波长双脉冲的三次谐波激光的产生 ,给出了相应的实验结果。     

星光Ⅱ装置激光能量测量实时采集和数据传输系统

介绍一套激光能量实时采集和多路传输通信系统。该系统兼容现有的不同型号和规格的激光能量计,具有峰值保持和功率积分功能,抗干扰能力强,可实现数据自动采集、处理及长距离多点传送。为实现激光能量测量精密化和自动化打下了技术基础。