基波激励和次谐波激励参量放大器特性的分析

本文主要结果有三:第一,推导出基波激励和次谐波激励参量放大器的优值、功率增益、和通带等主要特性,并就这些特性对基波激励源的和次谐波激励源的参量放大器进行比较;第二,通过半导体二极管非线性电容的谐波分量的分析,在激励电压、偏压和放大器的特性间得出定量关系,并且对给定放大器特性求出激励源幅度和频率的稳定要求;第三,推导出放大器的有效噪声,并给出最低有效噪声的设计条件。以上特性的探讨和二极管损耗、信号迴路和镜象迴路通带比、匹配等因子结合在一起进行,使所得结果更具有实际意义。最后举出一数字例子,说明应用本文结果来设计参量放大器的一种可能步骤。 关键词：     

行波式负阻放大器的相位及增益特性分析

由于各种固体负阻器件的进展,例如隧道二极管,参量应用的变容二极管等,从而引起了对具有周期性负载行波式分布放大器的研究。本文对这一类微波放大器的传输特性进行了详细分析,对其主要性能的分析包括:相位方程,增益方程,频率-相位关系,通带及阻带,相速及群速等等。文中给出了变容二极管行波式参量放大器的分析;还给出了重要的通用曲线及设计要点以供参考。 关键词：     

光子晶体光纤非线性系数与其结构参量及光波长的关系

推导计算了全内反射型光子晶体光纤的非线性系数与其两个几何结构参量:包层空气孔半径和空气孔间距之间的关系,给出了输入光波长为1550 nm处,非线性系数与这两个结构参量之间的关系曲线并对其进行了分析.给出了全内反射型光子晶体光纤的非线性系数随输入光波长变化的曲线,分析了短波处高非线性系数产生的原因并指出这一特性的应用潜力.     

高非线性光子晶体光纤色散特性的研究

采用矢量光束传输法对不同结构参量的高非线性光子晶体光纤的非线性特性和色散特性进行了数值分析,计算得出高非线性光子晶体光纤的物理参量基模有效面积Aeff 、非线性系数γ和色散系数D.分析了Aeff 、γ和D与高非线性光子晶体光纤结构参量空气孔间距Λ、空气孔直径d之间的关系.分析结果表明,通过调节光子晶体光纤的结构参量可以灵活地调整高非线性光子晶体光纤的非线性特性和色散特性.     

3～5μm角度调谐LiNbO3晶体光参量振荡器的技术研究

用LiNbO₃作参量晶体、调QNd:YAG(1.064μm)激光器做泵源,通过求出相位匹配点对有效非线性系数进行数值计算,找出有效非线性系数的最大值,从而求出该点对应的相位角和方位角,确定出进行角度调谐LiNbO₃晶体的切割角在理论计算过程中,用计算机模拟,得出了OPO的角度调谐曲线、有效非线性系数曲线和参量增益曲线实验研究中实现了369μm单点参量光输出,实验结果与理论计算结果相吻合.     

W波段二次谐波突变复合腔回旋管数值模拟

 通过对二次谐波低电压突变结构复合腔回旋管中谐振腔结构、模式竞争以及电子注-波互作用的研究,分析了高频结构特性、寄生模式的抑制和工作参数优化等问题。给出了3 mm 二次谐波低损耗TE₀₂/TE₀₃模式回旋管的模拟设计结果。计算采用了坡度磁场,互作用效率得到显著提高。PIC粒子模拟结果表明:在电子注电压25 kV、电流4 A、纵横速度比1.6、工作磁场1.72 T时,回旋管可获得37 kW 的输出功率,横向运动能量转换效率高达51%,器件效率为37%。     

光参量荧光寿命分布

 根据荧光寿命定义和放大过程获得的增益方程,研究了新型非线性晶体BaAlBO₃F₂中三种不同的相位匹配模式下中心波长532 nm泵浦的参量荧光光子寿命的分布特性。结果表明,当注入单色信号光时,参量荧光寿命随泵浦光相位匹配角的增加由椭圆体分布变化为圆环体分布。采用宽带信号光时,则由分散分布改变为集中在近200 nm波长范围内分布,并随泵浦光相位匹配角的增加而逐步减小。考虑宽带泵浦光注入情况时,参量荧光寿命的分布范围由于相位匹配范围增加而随之扩展。     

高Q Kerr介质腔中非关联双模相干态光场与V型三能级原子相互作用系统中光场的不等阶Y压缩效应

本文利用多模压缩态理论,研究了高QKerr介质腔中非关联双模相干态光场与V型三能级原子相互作用系统中双模光场的不等阶Y压缩效应,绘出了第一模“i(i＝1,2)”次方第二模“j(j＝2,3)”次方Y(i-j-Y)压缩度的第一正交分量(Sy_ij¹),第二正交分量(Sy_ij²)的时间演化曲线.结果表明:1)不等阶Y压缩特性强烈地依赖于Kerr介质的三阶非线性极化系数(x)和双模光场中各模的平均光子数n₁,n₂;当x<1,n₁=n₂<1时,不存在不等阶Y压缩效应;而当x＝2.5,5,10以及n₁=n₂=5,10时,光场和系统开始作用后的很短一段时间内呈现不等阶Y压缩效应.2)在x以及n₁,n₂不变的条件下,不等阶Y压缩度时间演化曲线的崩坍-复原时间随压缩阶次的升高而缩短,压缩度随压缩阶数,特别是两模幂次差的升高而迅速下降.3)在平均光子不变(即n₁=n₂恒定),但Kerr介质不同(即x变化)的条件下,不等阶Y压缩度曲线崩坍时间随Kerr介质的三阶非线性极化系数x的增加而缩短,幅度则不受Kerr介质的三阶非线性极化系数变化的影响.4)不等阶Y压缩效应的持续时间等强烈地依赖于Kerr介质的非线性程度,x越大不等阶Y压缩效应持续时间就越短.不等阶Y压缩度演化曲线正向幅度随平均光子数的增大而增大,负向幅度(压缩度)则随平均光子数的增加而减小.     

基于开口环的可调谐滤波器及其电磁带隙

基于开口谐振环上加载变容二极管设计可调谐滤波器,很好地实现了电磁波带隙的可调.在单环开口谐振环缝隙处或者双环开口谐振环的两环之间加载变容二极管,改变加载变容管上得的电压,改变该结构的分布参量而达到滤波器可调性能.同时通过数值计算分析了该滤波器结构对电磁波的频率响应函数,指出其形成电磁波带隙的物理机制,为了消除开口谐振环的磁谐振效应而关闭开口谐振环的缝隙实验进行了验证.研究表明基于变容管开口环的可调谐滤波器所形成的电磁波带隙中,有的带隙是源于磁谐振机制.有的带隙是源于电谐振机制.对该滤波器形成带隙物理机制的研究,可以更好地理解开口谐振环,有助于其在光学和微波波段器件的设计.     

利用变容管倍频的一些实验结果

Manlay从理论上证明:采用非线性电抗元件(例如变容管)进行倍频时,在理想情况下,可以获得100%的转换效率。已有的实验结果表明,经过周密设计的倍频器可以得到相当高的效率(例如,在三次谐波上获得了75%的效率。利用高效率的倍频器,可以获得极为稳定的微波讯号,用来观察和研究极窄的微波跃迁谱线,并加以利用(例如构成“原子钟”)。随着变容管性能的改善、倍频技术的发展,目前变容管倍频器已能得到足够的输出功率(χ波段达200mV,K波段40mV)而可以代替寻常使用的速调管,这种微波     

Theoretical performance of novel multipliers at millimeter and submillimeter wavelengths

A theoretical comparison of various low and high order multipliers for 200 GHz and 1 THz has been carried out. Novel diodes including single barrier varactors, barrier-intrinsic-n⁺ diodes and high electron mobility varactors are shown to have excellent theoretical performance, comparable or better than the conventional Schottky varactors for single and double diode frequency multipliers at millimeter and submillimeter wavelengths, whereas quantum well diodes, since they suffer from high resistive losses, are shown to be less attractive. In comparison to the conventional Schottky varactor, these new diodes have some potential advantages in their characteristics such as nonlinearity or a special symmetry. For future optimization some general comments on these advantages as well as other factors affecting multiplication is given.     

Parametric oscillator based on a single-layer resonant metamaterial

We perform numerical simulations demonstrating parametric generation and oscillation processes in a single-layer of metamaterial composed of split ring resonators (SRRs). In general, a parametric resonance is achieved by introducing a time-modulation of one of the energy-storing parameters of a resonant system. An individual SRR is a resonant system that can be modeled as an RLC-circuit inductively coupled to an applied time-varying magnetic field. The relatively simple circuit model can be employed to establish the range of parameters providing the growth of parametric oscillations within the SRR medium. We relate the numerically predicted circuit parameters that ensure the buildup of parametric oscillations to those parameters expected to be available in a modified SRR medium, in which lumped element varactors integrated into the SRRs are used as modulable capacitance elements.     

Excess capacitance of ZnO-Au varactors

Doped ZnO single crystals were deposited with gold and indium in 1×10^–8 Torr vacuum. The lithium-doped ZnO single crystals and the gold interface revealed not only a Schottky diode but also varactor characteristics. TheI-V andC-V characteristics of ZnO:Li-Au devices were determined in the 0–140 mV and 0–1.5 V ranges.The frequency dependence of ZnO:Li-Au varactors was investigated in the 6–550 kHz range and the value of the most efficient varactor frequency was found to be 50 kHz for the lithium-doped samples prepared.To bring further insight into the matter the concept of excess capacitance was introduced and 1/C ²=f(–V) curves were rearranged between 0–150 mV where Schottky characteristics are non-linear. The excess capacitance values of lithium-doped varactors were determined at four different frequencies and ranged from 26 pF at 50 kHz to 70 pF at 6kHz.Finally, the bulk donor concentrations of the single crystals were calculated from the modifiedC-V curves to beN _D= 3×10²⁰ m^–3. On the other hand, the bulk donor concentration determined from the non-modifiedC-V curves wasN _D=1.02×10²² m^–3.     

Studies of tunable four-photon parametric fluorescence of crystals in the visible region

Tunable four-photon parametric fluorescence, which is valuable for investigating material nonlinearities and parametric devices, was studied theoretically and experimentally.Theoretical analysis leads to the conclusion that the emitted power depends directly on the focusing of the pumping beam, unlike the process of three-photon parametric fluorescence which is independent of the focusing of the pumping beam. The calculation of the phasematching conditions for nonlinear crystals such as KDP, ADP, TiO₂ and CdS shows that collinear phase-matching can be realised over the visible region using a ruby laser for pumping. Experimentally, tunable emission was observed in the visible range from 4200 Å to 5300 Å with KDP and ADP crystals pumped by a Q-switched ruby laser.     

Millimeter wave monolithic high electron mobility (HEM) varactor diode-grid frequency tripler arrays

High Electron Mobility (HEM) varactor structures have been studied for millimeter-wave monolithic diode-grid frequency tripler array applications. The improved HEM varactor diode structures provide a highly nonlinear C-V characteristic (i.e., a steep slope of the C-V curve and a large capacitance ratio) which produces high harmonic generation efficiency and reduce the power requirement for efficiently pumping each device. The effects of the light illumination on the C-V characteristics of the Barrier-Intrinsic-N⁺ (BIN) varactor diode have also been studied and the results will be discussed in this paper. In the development of a monolithic diode-grid frequency multiplier array, the low-loss quasioptical configuration is used for the construction of the multiplier circuit. The study of the effects of the light illumination on the C-V characteristics of varactor diode is important in understanding the potential applications of the quasi-optical varactor diode-grid frequency multiplier array circuit.     

晶体热效应对LD端面泵浦固体激光器优化设计的影响

考虑了激光介质因受热不均匀而引起的热效应对激光器衍射损耗和谐振腔基模尺寸的影响,利用M²因子来描述泵浦光在激光介质中的传播规律,根据泵浦光在激光介质中的有效泵浦体积最小以提高泵浦效率这一判据,给出了含有泵浦光束质量因子M_p²和激光介质参量在内的端面泵浦固体激光器的优化设计曲线,利用这些曲线可方便地指导完成激光器的最佳化参量选择.利用上述理论,对LD端面泵浦光纤耦合输出的Nd:YVO₄激光器进行了研究,实验结果和理论分析相符合.     

Noncascading THz-wave parametric oscillator synchronously pumped by mode-locked picosecond Ti:sapphire laser in doubly-resonant external cavity

A noncascading terahertz (THz) wave parametric oscillator synchronously pumped by a mode-locked picosecond Ti:sapphire laser whose average power was less than 1 W was demonstrated with a noncollinear phase-matching MgO:LiNbO₃ crystal in an external enhancement cavity doubly resonant for both pump (780 nm) and signal (781-784 nm) waves. In the external cavity, in which the pump wave enhanced so as to reduce the pumping threshold of parametric processes, the signal wave could also resonate and thus be enhanced simultaneously, resulting in a THz wave output at approximately 0.9 THz as the idler wave. The novel dual enhancement of pump and signal waves reduced the threshold pumping intensity to approximately 50 MW/cm², which was much lower than that of a conventional externally pumped THz wave parametric oscillator with a crystal.     

Relevance of polarization phenomena in an optically pumped CF4 laser

Some applications of polarization phenomena in an optically pumped CF₄ lasers are reported. It is shown that the performance of a CF₄ laser can be greatly improved when the polarization characteristics of its optical cavity are chosen according to the types of transitions involved in the optical pumping and emission processes. It is also shown that polarization phenomena can be used to obtain an indication of the type of pumping and lasing transitions.     

Prospects for increasing average power of optical parametric chirped pulse amplifiers via multi-beam pumping

We demonstrate optical parametric amplification of broadband chirped pulses in BBO crystal pumped by several intersecting beams extracted from independent laser amplifiers. The energy of amplified signal ranged from 0.23 to 0.72 mJ depending on a number of pump beams used as well as pumping configuration employed. The conversion efficiency dependence on intersection angles of pump beams is revealed and modeling of interplay of interacting waves is presented.