光纤激光器时域瞬态特性的理论与实验研究

对掺铒光纤激光器的时域瞬态特性进行了理论与实验研究.理论模型从激光器的基本速率方程出发,通过求解增益光纤中的功率传输方程,得到激光器的时域输出结果.数值模拟了脉冲泵浦注入后激光器的瞬态特性,分析了激光器时域输出特性随泵浦功率及腔内损耗的变化规律.实验中采用上下沿功率均可调的方波泵浦掺铒光纤,通过可变光衰减器调解腔内损耗,观察激光器驰豫振荡特性,研究了激光建立的延迟时间与泵浦功率及腔损耗的关系.数值模拟与实验结果一致.     

聚合物微环谐振滤波器特性的研究

利用耦合模理论,计算了聚合物微环谐振滤波器的通路和下话路的传输函数,分析了耦合系数和损耗对传输函数的影响,并推导出了谐振滤波器的谐振波长、自由光谱范围、腔的品质因子、半峰全宽和精细度等特性参数,分析了不同的滤波器结构参数(如环形半径和有效折射率)对滤波特性的影响.     

矩形空心介质波导激光谱振腔的理论分析

本文发展了一种矩形空心介质波导激光腔的理论分析方法并给出其数值计算结果。这种方法采用多模近似理论,并以一个变换矩阵来表示腔内复杂的传输过程,使复杂的谐振腔模的特性得以简单而准确的描述。 通过对CO_2波导激光腔典型结构的计算,着重讨论了波导入口光斑尺寸对耦合效率的影响,球面反射镜参数与腔模特性的关系,最低损耗模的模式组成与模式选择性,平镜腔的近区特性以及波导结构、介质材料光学常数对腔模损耗特性的影响等;并对其中某些问题提出一些新的见解,为波导激光器的研究和设计提供了一系列有益的数据和结论。     

接触电阻和扭距序列作用下CICC耦合损耗模型

国际热核试验反应堆ITER和国内今后要建造的聚变工程实验堆CFETR上的CICC导体，将运行在大电流快速励磁的瞬变复杂磁场中，这使得中心螺线CS磁体上的导体会遭受10T以上的磁场冲击，目前已采用铌三锡(Nb₃Sn)材料，但应变对Nb₃Sn导体临界性能退化作用的研究还在探索中，同时更缺乏导体绞缆级扭距序列和股线接触特性对耦合损耗影响的实验分析研究.为此，在周期载荷模拟应变情况下，开展了不同扭距序列和导体接触电阻对耦合损耗作用的探索.研究分析表明，相对于经典耦合损耗和频谱损耗计算模型，由导体扭距序列比和接触电阻作用组合分析模型，计算获得的耦合损耗误差较小，与测试值最接近.结果显示采用扭距序列比和接触电阻组合的计算方法能取得较满意效果.     

耦合腔行波管SWS的尺寸变化对冷特性参量的影响

耦合腔行波管(CCTWT)慢波结构(SWS)的冷特性参量包括色散特性、耦合阻抗和分布损耗,是CCTWT研究与设计中的重要参量。本文利用CST微波工作室软件计算了CC TWT的SWS各个尺寸变化对冷特性参量的影响。这些影响不仅对CCTWT的设计有重要意义,而且为进一步研究相速渐变打下基础。     

耦合腔行波管中的切断匹配负载的设计和测量

介质谐振损耗腔用作耦合腔行波管切断处匹配负载，国内外已进入实用阶段，本文就此进行讨论，并给出了该介质腔谐振频率，介电常数，品质因素和损耗角的计算及测量方法，在研制一只Ｃ波段５０ｋＷ耦合的腔行波管中，理论与实则吻合，表明了本文理论分析和测量方法的有效性和可行性。     

选择损耗法抑制耦合腔行波管的带边振荡

利用选择损耗抑制耦合腔行波管的带边振荡是行之有效的方法.文中叙述了损耗钮扣型和谐振损耗器型两种选择损耗形式,后者在毫米波耦合腔行波管中得到了应用.     

基于稳定的时域积分方程方法对多天线辐射问题和互耦问题的研究

为有效地改善时间步进算法(MOT)的后时稳定性,引入类椭球波函数(APSWF)做为该算法的瞬态基函数.然而,基于此类瞬态基函数推导得到的系统具有非因果特性,因而必须使用外推方法以恢复时间步进算法的时间步进特性.采用所提出的方法对多天线结构进行数值仿真,获得其瞬态电流响应、回波损耗、耦合系数以及方向图等重要参数,实现了对天线辐射问题和互耦问题的分析与研究,同时也验证了本文所提出方法的有效性和精确性.     

小尺寸硅绝缘体光波导损耗测量

基于法布里-珀罗(F-P)腔理论建立了一种简单有效的硅绝缘体(SOI)光波导损耗测量方法.该方法采用端面耦合,通过测试波导反射功率谱并利用傅里叶频谱信息,完成波导损耗的测量.推导中指出了无法直接利用反射谱F-P峰峰谷值求解损耗的限制因素.应用该方法实现了对刻蚀深度为750 nm和宽度为1200 nm的SOI脊形波导损耗...     

圆波导激光器的腔片倾斜损耗

对采用平面反射镜的圆波导激光器的耦合情况进行了分析,提出腔镜倾斜引起损耗的计算模型,得到倾斜损耗的计算解析式和曲线。并对计算过程中取近似所忽略的部分也作了定量讨论,指出这种近似是可容许的。     

一种超宽带双信道速调管输出回路的设计和实验

该文介绍了一种超宽带双信道速调管输出回路的设计思路和实现过程。以Ansoft HFSS软件为设计平台,在S波段设计出一个带宽超过550 MHz的超宽带双信道双间隙耦合腔输出回路。设计了信道转换机构,并分别确定了两个信道的谐振腔参数。得出了不改变两个谐振腔参数,只需调节耦合槽的尺寸就能够实现信道转换的结论。通过对HFSS软件建立的模型进行计算,得到了双间隙耦合腔输出回路中各模式的频率,与冷测结果基本一致。利用集中元件等效电路法计算了双间隙耦合腔输出回路的间隙阻抗,计算结果与冷测结果基本一致。     

Comparative analysis of the Curnow and Malykhin-Konnov-Komarov (MKK) circuits as representations of coupled-cavity slow-wave structures

Two lumped element models of coupled-cavity slow-wave structures, one due to Curnow (1965) and another due to Malykhin, Konnov, and Komarov (MKK) (2003), are compared. The basis of comparison is the level of accuracy with which the models reproduce the cold circuit phase velocity and characteristic impedance of the structures as functions of frequency, as obtained from numerical solutions of Maxwell's field equations. Two distinct types of coupled-cavity structure are analyzed using these two models. These are a C-band double staggered ladder circuit and an L-band slot coupled "Hughes-type" structure. We find for the C-band case, both the Curnow and MKK models give excellent representations of both the cavity and slot bands, but for the L-band case the Curnow model has no solution when an attempt is made to fit both the cavity and slot bands, while the MKK model accurately represents both bands in this case.     

Novel high-gain, improved-bandwidth, finned-ladder V-bandtraveling-wave tube slow-wave circuit design

In this paper, the three-dimensional electrodynamic simulation code MAFIA (Solution of MAxwell's Equations by the Finite-Integration-Algorithm) is used to investigate methods of increasing the bandwidth and lowering the operating voltage of the ring-plane circuit. Calculations of frequency-phase dispersion, beam on-axis interaction impedance, attenuation, and small-signal gain per wavelength were performed for various geometric variations and loading distributions of the ring-plane TWT slow-wave circuit. Based on the results of the variations, a circuit termed the finned-ladder TWT slow-wave circuit was designed and is compared here to the scaled prototype ring-plane and a conventional ferruled coupled-cavity TWT circuit over the V-band frequency range. The simulation results indicate that this circuit has a much higher gain, significantly wider bandwidth, and a much lower voltage requirement than the scaled ring-plane prototype circuit, while retaining its excellent thermal dissipation properties. The finned-ladder circuit has a much larger small-signal gain per wavelength than the ferruled coupled-cavity circuit, but with a moderate sacrifice in bandwidth     

MAGIC3D Simulations of a 500-W Ka-Band Coupled-Cavity Traveling-Wave Tube

The 3-D particle-in-cell (PIC) simulations of a Ka-band coupled-cavity traveling-wave tube (CCTWT) are shown. The computational analysis of the Ka-band coupled-cavity slow-wave structure was conducted through the use of an electromagnetic PIC code MAGIC3D. The choice of a double-slot staggered RF cavity circuit was made because of a wide frequency bandwidth, moderate interaction impedance, and excellent thermal dissipation properties. We investigated the large-signal and nonlinear beam dynamics of a Ka-band CCTWT using MAGIC3D. The center frequency of the Ka-band CCTWT can be tuned from 28.4 to 30 GHz by varying the cathode voltage. Hot-test simulations show that the 84-cavity Ka-band CCTWT produces 540 W of saturated output power at 29 GHz with an electronic efficiency of 8.1% and a gain of 28 dB when the beam voltage and current are set to 17 kV and 390 mA, respectively.      

Wavelength self stabilisation of coupled-cavity semiconductor lasers

A simple wavelength control circuit is demonstrated that maintains single-longitudinal-mode operation of coupled-cavity semiconductor lasers over wide ranges of temperature. Photodetection properties of the lasing system itself are used for generating the discriminating signal for the feedback loop. No external optical elements like photodetectors or spectrometers are required.     

A coupled-monotron analysis of band-edge oscillations in high-power traveling-wave tubes

A theoretical analysis of the interaction of an electron beam with a coupled-cavity structure near a band-edge frequency is presented. The analysis utilizes the resonant modes of the individual cavities in a way such that the details of the electronic interaction within each distinct cavity are identical to those of the monotron theory, but the coupling between adjacent cavities is taken into account via the circuit equations. There arenequations obtained forncavities, and an algebraic rather than a characteristic wave type of approach is chosen for their solution. The theory is applied to finding the starting conditions for band-edge oscillations in an untapered structure. The results are verified experimentally. The theory also indicates that it is probably valid to use the simple monotron theory to find the minimum start-oscillation length or current.     

An Equivalent Circuit for the "Centipede" Waveguide

An equivalent circuit is presented for the "centipede" coupled-cavity waveguide. The "centipede" waveguide, which is typical of the class of slow-wave structures suitable for use in a wide-band high-power traveling-wave tube, has two pass bands which may interact strongly with a small-diameter electron beam. The equivalent circuit is able to represent both of these pass bands. A detailed comparison with an S-band "centipede" waveguide shows that the equivalent circuit can represent the dispersion, interaction, and loss characteristics of the waveguide within a few percent.     

A Stabilized MIC Oscillator Using a Germanium Avalanche Diode (Short Papers)

A stabilized X-band oscillator using a germanium avalanche diode in a microwave integrated circuit (MIC) is proposed. The stabilization is achieved by coupling a transmission cavity to the resonant cavity in which an avalanche diode is embedded. A mode-jumping problem inherent in a coupled-cavity oscillator was solved coupling a third varactor-embedded low-Q cavity to the transmission cavity. As a result, single-mode oscillation in an MIC oscillater was successfully obtained. Varactor tuning can also be realized with as small a change in output power as 7 percent for a tuning range of 30 MHz. The experimental results and the theoretical analysis of the new stabilized oscillator are given.     

Design of high-efficiency wide-bandwidth coupled-cavitytraveling-wave tube phase velocity tapers with simulated annealingalgorithms

The output circuit section of a traveling-wave tube (TWT) routinely contains an RF phase velocity taper for the purpose of increasing RF output power and efficiency. By slowing the RF phase velocity in approximate synchronism with the decelerating electron beam bunches, the taper increases power transfer from the beam to the RF wave. Recently, the computational optimization technique of simulated annealing was shown to be very effective in the design of an RF phase velocity taper that significantly increased computed RF power and efficiency of a coupled-cavity TWT. In this paper, two new broadband simulated annealing algorithms are presented that optimize (1) minimum saturated efficiency over a frequency bandwidth and (2) simultaneous bandwidth and minimum efficiency over the frequency band with constant input power. The algorithms were incorporated into the NASA 2.5-dimensional (2.5-D) coupled-cavity TWT computer model and used to design optimal phase velocity tapers using a 59-64 GHz coupled-cavity TWT as a baseline model. Compared to the baseline taper design, the computational results of the first broadband algorithm showed an improvement of 73.9% in minimum saturated efficiency. The second broadband algorithm indicates an improvement of 272.7% in minimum RF efficiency with constant input power drive and an increase in simultaneous bandwidth of 0.5 GHz over that calculated for the baseline TWT     

准周期边界条件法在耦合腔结构高频特性研究中的应用

该文指出准周期边界条件法在耦合腔高频特性研究的应用中会出现伪解,提出了相移法和能量法对伪解进行辨别,并初步探讨产生伪解的原因,然后提出了去除伪解的理论分析法和相移法,其中相移法具有普遍性。最后给出了该方法在休斯型耦合腔结构中的应用算例。