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     

基于PPLN光波导和频与差频级联型全光波长转换的研究

介绍了基于准相位匹配周期极化反转铌酸锂光波导的和频与差频(SFG DFG)级联型全光波长转换技术的基本原理.计算了SFG DFG级联型波长转换的转换效率,分析了抽运光功率以及两个抽运光之间的间距对转换效率的影响,抽运光功率越大,转换效率越高;转换效率随着间距的增大先增大后减小.单抽运调节时的抽运带宽为0.5 nm,同时对信号光脉冲还有压缩作用,压缩比是0.68.     

准相位匹配级联二阶非线性全光波长转换研究

对基于级联和频差频非线性效应铌酸锂光波导新型全光波长转换器进行了理论研究。这种新型波长变换器需要两束抽运光源,它将输入的抽运光波长置于信号光波段窗口的两边,抽运光波长与信号光波长相近容易实现最佳耦合又不会占用信号波段,而且具有偏振不敏感的优点。从建立级联和频差频铌酸锂光波导全光波长转换器的理论模型出发,给出了波导中光相互作用的耦合模方程;利用逐步法详细推导了耦合模方程的解,得出了物理意义清晰的转换光功率表达式,分析了非线性晶体相互作用长度、抽运光功率对转换效率的影响,为级联和频差频铌酸锂光波导全光波长转换器优化设计提供了理论依据。     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

光纤型宽带可调连续波差频产生中红外激光器转换效率的研究

以掺镱光纤激光器为抽运源、掺铒光纤激光器后接掺铒光纤放大器为信号源,利用周期极化掺镁铌酸锂晶体,研究了全光纤化差频产生中红外激光器的转换效率特性。结果表明,抽运光和信号光偏振态影响差频产生过程的转换效率,利用偏振控制器,可将抽运光和信号光偏振方向调节到与晶体光轴方向平行,以获得高的转换效率。抽运光和信号光的光束质量既影响差频产生过程的转换效率,又决定晶体纵向位置的容限,当聚焦系统由自聚焦透镜和焦距100mm平凸透镜组成时,相对转换效率达0.717mW-2,晶体纵向位置容限为44mm。此外,差频光在3126.36~3529.6nm范围内调谐时,转换效率基本保持不变。     

基于周期极化反转铌酸锂光波导高速非归零码到归零码的转换

研究了基于周期极化反转铌酸锂光波导级联二阶非线性效应实现非归零码到归零码高速全光码型转换的新方案,使用的是马赫-曾德尔干涉仪结构.转换原理是非归零码信号光在级联倍频和差频过程中受到的放大作用引起马赫-曾德尔干涉仪的不平衡,进而通过干涉相消产生归零码信号光输出.首先从耦合波方程出发,数值模拟了非归零码到归零码码型转换过程.然后分析了波导长度、光功率、相对时延对消光比的影响并对码型转换进行了优化设计.最后分析了转换带宽,模拟计算表明信号光在90nm的3dB带宽内可调谐,进而可以实现多信道的同时转换. 关键词： 码型转换 级联倍频和差频 周期极化反转铌酸锂 马赫-曾德尔干涉仪     

基于和频与差频级联的全光单光子波长变换

基于周期极化铌酸锂波导,提出了一种采用和频产生与差频产生级联的全光单光子波长变换方案.在海森堡绘景下,通过非线性变换过程的哈密顿量求解了目标单光子信号的湮灭算子,进而根据变换前后的光子数算符之比得到了单光子波长变换的效率.分析了和频产生过程以及差频产生过程中单光子的转换效率与泵浦功率之间的关系,证明了存在最佳泵浦功率使得量子态能够完全转移.数值分析结果表明,当上变换(和频产生)泵浦光功率为65 mW、下变换(差频产生)泵浦光功率为150 mW时,由1550 nm到1530 nm的单光子波长变换可达到61％的转换效率.给出了级联单光子波长变换的实验装置,包括周期极化铌酸锂波导、泵浦激光、准单光子信号源、滤波等光学元器件、单光子探测器和同步线路.     

1.5μm波段基于级联二阶非线性的铌酸锂光波导全光波长变换的理论分析

研究了基于级联二阶非线性的铌酸锂波导全光波长变换器的特性.首先从耦合模方程出发,比较了数值分析结果与小信号近似分析的结果.其次在数值分析基础上,分析了铌酸锂晶体的温度变化导致相应基频光波波长与极化反转光栅周期的变化关系.最后分析了在不同相互作用长度下,转换的光波功率与有效基频光波波长带宽、温度调谐带宽、极化反转光栅周期带宽等关系,以对全光波长变换器件进行优化设计 关键词： 级联二阶非线性 波长变换 准位相匹配 铌酸锂光波导     

宽带准连续光纤激光在周期极化铌酸锂中倍频特性的研究

双包层光纤激光器和非线性光学材料(如周期性极化的铌酸锂晶体,PPLN)相结合,开辟了实用性非线性光学器件的一个新领域。研究了准相位匹配周期性极化反转铌酸锂晶体对宽带准连续光纤激光倍频的温度特性和频谱特性。在理论上,从准相位匹配相位失配关系出发,推导了晶体温度与抽运源中心波长的关系以及温度响应带宽,并和已报道实验结果进行了比较,二者符合得很好。此外,还推导了倍频周期极化铌酸锂晶体对抽运基频光源的响应谱线带宽。在实验上,采用长度20mm,极化周期6．5μm,厚度0．5mm的周期极化铌酸锂晶体光纤激光器准连续宽带输出进行了倍频,获得了在不同控制温度下的倍频光光谱,并对此进行了详细分析。     

Experimental observation of tunable wavelength down- and up-conversions of ultra-short pulses in a periodically poled LiNbO3 waveguide

All-optical tunable wavelength conversion of ps-pulses is proposed and experimentally demonstrated by use of cascaded sum- and difference frequency generation (cSFG/DFG) in a periodically poled LiNbO₃ (PPLN) waveguide. The amplified spontaneous emission (ASE) noise is effectively suppressed by employing two tunable filters. As a result, tunable wavelength down- and up-conversions are simultaneously observed. The temporal evolutions of the signal, pump, control and idler waves propagating along the PPLN waveguide are simulated. From the temporal waveforms and optical spectra in the simulations, it is interesting to find that continuous wave (CW) pump and control are evolved into optical pulses during the cSFG/DFG nonlinear interactions. Moreover, some new sidebands in the output pump spectrum are observed both in the simulations and experiments.     

Polarization Insensitive Wavelength Conversions by a LiNbO3 Waveguide Using a Multi-Ring Configuration

A novel configuration is proposed for polarization insensitive wavelength conversions using a LiNbO₃ waveguide with a periodically domain inverted structure. The proposed configuration consists of multiple rings, which are connected by a polarization sensitive wavelength converter such as the LiNbO₃ waveguide described. One ring containing a pump light source is used to pump the wavelength converter bidirectionally, while the other rings containing a polarization beam splitter and a 90° polarization rotator are used to couple in the input signal and extract the converted light. The proposed method is proven experimentally by the wavelength conversion based on sum frequency generation.     

在周期性极化铌酸锂波导中的波长转换与光谱分析

实验研究了在准相位匹配LiNbO₃波导中级联的倍频和差频波长转换,通过对转换频谱分析和波形对比分析,讨论了在脉冲泵浦情况下走离效应对光脉冲之间波长转换的影响：由于波导的色散性能,不同波长的光脉冲在波导中传播具有不同的群速度,处在0.8 μm光波段的倍频光脉冲比处在1.55 μm光波段的泵浦光脉冲的传播速度慢,导致了倍频光脉冲与泵浦光脉冲在传播的过程中发生走离;因此倍频脉冲在频域被压缩而在时域被展宽,并遗传给差频过程使得转换脉冲的谱宽变窄、脉宽增加、占空比变大,表明脉冲光泵浦波长转换对信号频谱及波形不是严格透明的转换。实验同时实现了一对多通道的波长转换,表明连续控制光的线宽对转换信号的信噪比有较大的影响。     

Polarization-insensitive all-optical wavelength conversion of 320 Gb/s RZ-DQPSK signals using a Ti:PPLN waveguide

Polarization-insensitive wavelength conversion of a single channel 320 Gb/s RZ-DQPSK data signal using a Ti:PPLN waveguide in a bi-directional loop configuration with less than 0.5 dB polarization sensitivity is reported. The conversion efficiency with polarization scrambling of the signal was ?21 dB, which includes 9.2 dB of passive losses in the whole Ti:PPLN subsystem. In BER measurements error-free operation with 2 dB OSNR penalty for the converted signal was achieved. Theoretical and experimental investigations of the temporal shape and chirp of the converted data pulses show only very little broadening and chirping, indicating the potential for wavelength conversion of even much higher data rates.     

All-optical wavelength tuning in Ti:PPLN Šolc filter via the photorefractive effect

We demonstrate fine-wavelength tuning of a periodically poled Ti:LiNbO₃ (Ti:PPLN) Šolc filter by use of the photorefractive (PR) effect. The center wavelength of a Ti:PPLN Šolc filter is controlled by the PR effect, which is induced by second-harmonic generation (SHG). The refractive index change caused by the PR effect is calculated from the measured shift in center wavelength from the Ti:PPLN Šolc filter. The experimental results show that all-optical fine-wavelength tuning in a Ti:PPLN Šolc filter is possible by the use of a second-order nonlinear effect and that a Ti:PPLN waveguide has much higher resistance to PR damage than a Ti:LiNbO₃ waveguide. The measured wavelength tuning rate as a function of the pump beam power is about − 0.033 nm/mW.     

Fiber-feedback continuous-wave and synchronously-pumped singly-resonant ring optical parametric oscillators using reverse-proton-exchanged periodically-poled lithium niobate waveguides

We describe guided-wave singly-resonant reverse-proton-exchanged (RPE) periodically-poled lithium niobate (PPLN) waveguide ring optical parametric oscillators (OPOs) in which the feedback was provided via a single-mode fiber pigtailed to the waveguide. Wavelength selection was achieved by means of a fiber Bragg grating inside the feedback loop. The SRO threshold for the synchronously-pumped OPO was below 1 mW of average coupled pump power.     

Continuous wave,singly resonant MgO:PPLN OPO pumped by a Nd:YVO<Subscript>4</Subscript>/YVO<Subscript>4</Subscript> ring laser

A continuous wave (CW), extra-cavity singly resonant optical parametric oscillator (SRO) has been demonstrated. The SRO is based on 5% magnesium-oxide doped periodically-poled lithium niobate (MgO:PPLN) pumped by a CW Nd:YVO₄/YVO₄ ring laser centered at 1064.4 nm. The nonlinear crystal temperature is kept at 120.0 ± 0.1°C and a domain period of 30 μm is used in this experiment. When the pump power is 11 W, an output power of 2.0 W at the idler wavelength of 3.479 μm has been obtained from the OPO. The optical-optical conversion efficiency is about 18.2%, and the slope efficiency is about 20.8%.