周期性极化铌酸锂晶体中半非共线型宽带光学参变放大理论研究

基于周期性极化铌酸锂晶体(PPLN)的准相位匹配光参变放大过程,通过倾斜周期极化铌酸锂晶体中极化域(极化光栅)一定角度,实现了介于共线匹配方式和非共线匹配方式之间的一种半非共线型准相位匹配方式,并以该匹配方式下的各光矢量几何关系得出相位匹配曲线,找到在特定抽运光和信号光波长下能获得宽带增益放大的周期极化长度。并研究其极化倾斜角度与温度特性。模拟计算表明,在合适的角度与温度条件下,该方式可以532 nm抽运光抽运的信号光在800 nm和1064 nm处均获得宽带光参变放大。     

抽运光角度调谐准相位匹配光学参量振荡器的研究

针对利用周期极化晶体实现的抽运光角度调谐准相位匹配(QPM)光学参量振荡器(OPO)进行了系统的理论分析，给出了描述QPM OPO中抽运光旋转角与三波波长关系的精确公式和近轴公式.研究发现，对信号光单谐振的情况而言，抽运光与空闲光沿晶体x轴的同侧出射，而对空闲光单谐振而言，抽运光与信号光沿晶体x轴的同侧出射.另外，信号光单谐振下信号光与空闲光间的夹角要大于空闲光单谐振下两者间的夹角.更重要的是，信号光单谐振时的波长调谐速度也较空闲光单谐振时的大. 关键词： 准相位匹配 空闲光单谐振光学参量振荡器 抽运光角度调谐 调谐速度     

双共振准相位匹配光学参量振荡器的调谐特性

利用全固化单频Nd：YVO4激光器泵浦双共振难相位匹配铌酸锂连续光学参量振荡器，实验研究了该光学参量振荡器下转换光的调谐特性。通过改变PPLN晶体的温度及OPO的腔长，下转换光的调谐范围分别为189nm和175nm，通过改变泵浦光频率，信号光频率连续调谐375MHz。实验结果与理论计算值基本吻合。     

利用宽带倍频特性精确测量准相位匹配晶体的极化周期

 提出了利用准相位匹配晶体进行宽带脉冲倍频，再根据准相位匹配晶体的极化周期与倍频脉冲输出中心波长的相位匹配关系来精确测量准相位匹配晶体极化周期的新方法。理论分析了准相位匹配晶体的极化周期与倍频脉冲的光谱关系、倍频容许带宽与晶体长度的关系。研究表明：宽带脉冲倍频后输出的脉冲峰值波长对应于角度的调谐曲线具有对称性；对于长度为10 mm的极化晶体，其倍频容许带宽不到0.2 nm。实验中，采用了国产PPKTP晶体试验片，晶体尺寸为10 mm×7 mm×1 mm，理想极化周期9 300 nm。结果表明：对于中心波长为537.25 nm的倍频光，其对应的实际晶体极化周期为9 303.9 nm，大于晶体加工时的理想值；当倍频脉冲光谱测量精度为0.01 nm时，准相位匹配晶体的极化周期测量精度达到0.1 nm，远高于一般光学显微镜的观测精度。     

理论构造周期极化KTiOPO_4晶体制备852和1550nm双色纠缠光

利用KTiOPO4(KTP)材料非线性系数d33对应的二阶非线性0-类准相位匹配,理论上设计构造了一种周期极化KTiOPO4晶体(PPKTP),当晶体温度为20℃时,晶体准相位匹配格子的周期为10.70μm。波长为550nm的激光泵浦由该晶体组成的光学参量振荡器能产生含852nm信号光和1550nm的闲置光的双色纠缠,其中信号光对应Cs原子吸收线,闲置光1550nm对应光纤通讯波长。该纠缠光对量子信息网络和原子信息存储有非常重要的意义。     

基于准相位匹配晶体的宽带可调谐光参量放大过程研究

系统分析了基于准相位匹配晶体的光参量放大过程中极化周期和非共线结构对信号光调谐带宽的影响.提出了最大极化周期的概念,用于描述非共线相位匹配和群速度匹配同时满足时晶体的极化周期所能达到的最大值,给出了用于计算不同温度下周期极化铌酸锂晶体的最大极化周期的数学公式,并确定了宽带可调谐光参量放大过程应使用的最佳非共线结构.当采用此非共线结构时,通过将晶体的极化周期设定为最大极化周期可以在相对最大的波长范围内实现信号光的调谐放大输出.在此基础上提出了一个用于最大化光参量放大过程的信号光调谐带宽、确定工作温度等最佳工作参数以及简化实验操作方法的可行性方案.最后对最大极化周期和非共线结构对光参量放大的参量带宽的影响进行了研究. 关键词： 光参量放大 极化周期 非共线结构 带宽     

周期性极化铌酸锂晶体光参量振荡调谐与容差特性分析

研究了周期性极化铌酸锂晶体光参量振荡的工作机理,并讨论了其波长调谐特性与极化反转光栅周期、抽运光波长与晶体温度的关系.在此基础上,通过对相位失配因子求微分的方案,分析了光参量振荡的增益与光栅周期、抽运光波长与晶体温度的关系,以及光栅周期、抽运光波长与晶体温度容差的关系 关键词： 准相位匹配 周期性极化铌酸锂 光参量振荡     

新颖的PPLN电光开关

在分析基于级联二阶非线性效应的准相位匹配周期极化铌酸锂(PPLN)波导全光波长变换器的有关参量容限的基础上,提出PPLN波长变换器的电光调控设想,并给予简要论证,论证结果是可行的,从而可实施电控调谐来自动补偿其失配,进而也可实现光开关的功能 关键词： 准相位匹配 周期极化铌酸锂 波长变换 光开关 电光效应调控     

周期极化铌酸锂THz波产生理论分析

首先采用光参量振荡的机理研究了THz波在准相位匹配媒质周期极化铌酸锂晶体中同向传播与反向传播情况下,以及THz波从晶体表面辐射产生的特性;其次研究了THz波的温度调谐特性、极化反转光栅周期调谐以及改变入射泵浦光与光栅波矢夹角的调谐特性;然后分析了THz波谱宽特性,给出解析表达式,并与实验结果进行了比较,证明理论分析结果与Y.S.Lee等人所给出的实验结果符合很好;最后分析了THz波的稳定性与温度、光栅周期、泵浦入射角以及辐射角的关系.     

宽波段连续调谐全固态CW PPMgLN光学参量振荡器

利用半导体激光泵浦输出1064 nm波长的全固态连续Nd:YVO4激光器作为泵浦源,采用周期调谐和温度调谐组合调谐技术,对基于掺氧化镁周期性极化铌酸锂晶体（MgO:LiNbO3, PPMgLN）准相位匹配（QPM）的全固态连续波（CW）光学参量振荡器（OPO）宽波段无分立连续调谐输出特性进行研究。实验采用连续工作模式和外腔结构,基于多周期PPMgLN晶体的30.2,30.4和30.6 m周期,在改变晶体的极化周期的基础上,同时在30～100 ℃范围内调节晶体工作温度。实验结果表明:CW PPMgLN OPO的泵浦阈值仅为0.22 W;不同极化周期需要的温度调谐范围不同;信号光在1 559.8～1 597.2 nm近红外波段和闲频光在3 187.3~3 347.3 nm中红外波段连续调谐输出。实现了外腔式全固态CW OPO在信号光和闲频光波段的无分立连续调谐输出。     

Tolerance and tuning properties of the optical parametric processes using periodically poled RbTiOAsO4

The maximal tolerance parameters of poling period and phase-matching, temperature in second harmonic generation (SHG) using periodically poled RbTiOAsO₄(PPRTA) as a function of the fundamental wavelength are investigated theoretically. The tolerance of the poling period ΔΛ of PPRTA is found larger than that of PPLN and PPKTP when the fundamental wavelength is beyond 2 μm, which reaches its maximum ΔΛ_max for PPRTA at a fundamental wavelength of 2.7433 μm. However, the tolerance for the phase-matching temperature ΔT of PPRTA is found smaller than that of PPLN and PPKTP with an exception that PPRTA has a larger tolerance of the temperature or a larger temperature phase-matching bandwidth at fundamental wavelength of 2.2474 μm, where the maximum of ΔT(ΔT_max) is obtained. Furthermore, the tuning characteristics of the optical parametric processes using PPRTA for collinear quasi-phase-matching (CQPM) is analyzed. The combination of temperature tuning and poling period tuning enables a quasi-continuous wavelength tuning range of 1493.2-1593.7 nm for the signal and 3201.8-3699.2 nm for the idler, where poling period of 39 μm, 39.5 μm and 40 μm and a temperature between 20 and 120° have been employed in the corresponding theoretical analysis.     

周期极化KTP晶体光参量振荡特性研究

基于较新的Sellmeier方程,研究了周期极化钛氧磷酸钾(KTiOPO₄简称KTP)晶体光参量振荡的容差特性,给出了极化反转光栅周期、晶体温度及泵浦光波长的调谐曲线和带宽的容差特性曲线,并与PPLN晶体作了比较数值计算结果与已有实验数据吻合较好.     

Optical parametric oscillators for high pulse energy and high average power operation based on large aperture periodically poled KTP and RTA

We report on optical parametric oscillators (OPOs) based on large aperture periodically poled KTiOPO₄ (PPKTP) and RbTiOAsO₄ (PPRTA) pumped with high pulse energy and high average power Q-switched solid-state lasers. The OPOs were pumped with 1064-nm pulses of a diode-pumped Nd:YVO₄ laser at 20 kHz repetition rate. The emitted signal wavelengths were 1.72 μm and 1.58 μm and the idler wavelengths were 2.79 μm and 3.26 μm, respectively. Pumping the PPKTP OPO with 7.2 W and the PPRTA OPO with 8 W average power, 2 W and 1.3 W total OPO output powers were generated. Two-dimensional measurements of the total OPO output power, the signal wavelength and the signal bandwidth in dependence on the crystal location indicated a good uniformity of the quasiphasematching structure over the entire 3-mm-thick crystals. This allowed pumping with larger pump beams and therefore with pulse energies of tens of millijoules. Pumping with different flash-lamp-pumped lasers, good OPO performance and high output pulse energies could be achieved for all pump lasers. Maximum input pulse energies of 56 mJ gave output pulse energies of as much as 18 mJ. The temperature tuning behaviors of both OPOs were measured, showing excellent agreement with calculated temperature tuning curves. New equations for temperature dispersion in RTA are presented. These results show that large-aperture PPKTP and PPRTA crystals are well suited for tunable nanosecond OPO operation with multi-watt average pump power and several tens of millijoules pump pulse energies. Received: 7 September 2001 / Published online: 7 November 2001     

周期极化铌酸锂中通信波段纠缠双光子的波长管理方法

理论研究了周期极化铌酸锂晶体中通过自发参量下转换产生的纠缠双光子的波长管理方法.简并自发参量下转换产生的单色偏振纠缠双光子的波长,可以通过调整晶体的极化周期或工作温度自由地调节,特别是在加工好的晶体中极化周期是确定的,因而调整晶体的工作温度更加便捷.对于双色偏振纠缠双光子来说,不需改变入射的泵浦光以及晶体的极化结构,仅通过调节晶体的工作温度就可以实现o光光子和e光光子波长的严格交换.     

Study of quasi-phase matching wavelength acceptance bandwidth for periodically poled LiNbO3 crystal-based difference-frequency generation

The temperature tuning characteristics of quasi-phase matching (QPM) wavelength acceptance bandwidth in a uniform periodically poled lithium niobate (PPLN) based on difference-frequency generation (DFG) are studied theoretically and experimentally. This paper proposes a PPLN device consisting of several segments of different temperatures to obtain a more desirable performance for the QPM-DFG. The result shows that through the tuning of temperature, the bandwidth can be changed considerably and the method was proved suitable and accurate to calculate QPM wavelength acceptance bandwidth of DFG in a uniform PPLN crystal for temperatures between room temperature and 180 °C and mid-infrared (mid-IR) wavelengths ranging from 2.8 to 4.8 μm.     

Widely tunable difference frequency generation around 3.4 μm using index dispersion property of PPLN

In this paper, the wide difference frequency generation (DFG) tuning characteristics around 3.4 μm are investigated by using the index dispersion property of PPLN. With a ytterbium doped fiber laser (YDFL) and an erbium doped fiber laser (EDFL) as the fundamental light sources, our simulation results show that the quasi-phase matching (QPM) wavelength acceptance bandwidth (BW) for the pump is much larger than that for the signal. Although the positions of the broadened QPM pump bands vary with the poling period and the signal wavelength, the corresponding idler tuning ranges center around 3.4 μm. With a signal wavelength of 1.57 μm, an idler tuning range of greater than 170 nm is experimentally obtained in the 30 uniform grating PPLN. When the signal wavelength and the poling period are respectively changed to 1.55 and 29.50 μm, wide DFG tuning operations around 3.4 μm are also achieved with the crystal temperature adjusted to adapt the change.     

Theoretical and experimental investigations of the Mid-IR DFG tuning property based on fiber laser fundamental lights

The tuning properties for the mid-IR DFG laser based on uniform grating PPLN have been investigated with tunable YDFL and EDFL fundamental lights. Our results show that, for a fixed crystal temperature, the idler tunable range is less than 10 nm when the EDFL is tuned. Although the pump may be allowed to be tuned in its two QPM acceptance bands, the idler tunable range is still narrow for a fixed temperature. By optimizing the crystal temperature, however, the two pump QPM acceptance bands may be overlapped to form one broadband QPM band, which may be used to increase the idler tunable range to 175 nm near 3.4 μm region. The positions of the single signal and the two separate pump QPM acceptance bands can be continuously moved by adjusting the temperature, which may also be used for enhancing the idler tuning range. By tuning the EDFL while adjusting the temperature, a whole combined idler tuning range between 2.98 and 3.78 μm was experimentally obtained with three fixed pump wavelengths of 1.05, 1.08 and 1.11 μm. By tuning the YDFL in the two separate QPM acceptance bands, a tuning range of 690 nm has been demonstrated with only one fixed signal wavelength of 1.58 μm.     

Collinear broadband optical parametric generation in periodically poled lithium niobate crystals by group velocity matching

Collinear broadband optical parametric generation (OPG) using periodically poled lithium niobate (PPLN) crystals were designed and experimentally demonstrated with the quasi-phase matching (QPM) periods of 21.5, 24.0, and 27.0 μm. The broad gain bandwidth was accomplished by choosing a specific set of the period and the pump wavelength that allows the group velocities of the signal and the idler to match close to the degeneracy point. OPG gain bandwidth and also the spectral region could be controlled by proper design of QPM period and pump wavelength. The total OPG gain bandwidth of 600, 900, and 1200 nm was observed for the PPLN devices with QPM periods of 21.5, 24.0, and 27.0 μm, respectively. We have also observed multiple color visible generation whenever the OPG spectrum was significantly broad. From the visible peaks of the three PPLN samples, it is found that broad gain bandwidth is crucial in the temperature-insensitive collinear simultaneous RGB generation from a single crystal.     

Widely tunable mid-IR difference-frequency generation based on fiber lasers

A wide tuning technique for mid-IR difference-frequency generation (DFG) with uniform grating periodically poled LiNbO(3) (PPLN) is presented. Based on the dispersion property of the PPLN, the quasi-phase matching (QPM) band for the pump can evolve to two separate bands, and the spacing between them can be increased with the decrease of the crystal temperature. Two such separate QPM bands can be used for increasing the idler tuning range when the crystal temperature is set to adapt the pump tuning. With the technique, an idler tuning range of 690nm is experimentally achieved with fiber laser fundamental lights.     

Angle-tuned second-harmonic generation in periodically-poled lithium niobate

We investigated angular tuning of quasi-phase-matching (QPM) second-harmonic generation (SHG), in order to extend the tunable range of QPM and to combine the advantages of QPM and birefringence phase-matching. The direction of the input fundamental wave vector was detuned from the QPM grating vector along the crystallographic Z-axis of a periodically-poled lithium niobate (PPLN) crystal in the XY- and XZ-planes. A?larger tuning range of SHG was obtained for the detuning in the XZ-plane, continuously shifting the QPM peak of the fundamental wavelength from 1524 to 1595?nm by changing the detuning angle from 0° (parallel to X-axis as conventional QPM) to 23.2°.