锥形光纤的结构与特性

通过理论分析和仿真试验,研究了锥形光纤的几何形状对锥形光纤的传输损耗和耦合效率的影响.用几何光学的分析方法,说明了光信号在锥形光纤中的传输损耗远低于同类型的圆柱形光纤;仿真试验研究了光源与光纤的相对位置、锥形光纤的尖端半径、锥形光纤的锥角大小对锥形光纤耦合效率的影响.     

Beam propagation analysis for tapered waveguides: taking account ofthe curved phase-front effect in paraxial approximation

A novel equivalent waveguide theory based on the conformal mapping method is employed to investigate the tapered waveguide with curved phase fronts. By using the theory, the curved phase fronts of a tapered waveguide would be transformed into the planar ones of its equivalent straight-liked structure. Therefore, the paraxial beam propagation method can be used to analyze the equivalent structures of tapered waveguides (even for wide-angle tapers). Two kinds of popular tapered waveguides, including the cross-sectional dimension tapering and the constant V-number tapering, are used to analyze by our combination of conformal mapping method and beam propagation method (BPM)     

锥形过渡波导的光束传播法分析

基于光束传播法,对几种只沿纵向变化的锥形过渡波导的传输特性进行了分析.分析表明,对同一过渡波导,宽端口输入与窄端口输入时的功率损耗不同,因而应根据过渡波导是宽端口输入还是窄端口输入来选用过渡波导.波导参数对各种过渡波导传输特性的影响也不同.分析结果为各种过渡波导的选用提供了参考.     

锥形光纤传输特性的检测与分析

在实验上用剪断法测量锥形光纤的传输效率随锥形光纤圆锥角的变化关系，作出传输效率曲线；根据标量波动方程，运用高斯近似法，从理论上说明光信号在锥形光纤中的传输特性和能量损耗，并用具体数据进行半定量计算。结果表明，锥形光纤顶端锥体的角度及其变化愈大愈光滑，锥形过渡区越短，传输效率就越高。     

Assessment of coupled-mode theory for tapered optical coupler

The accuracy and the scope of validity of different coupled-mode formulations for a tapered optical waveguide coupler are assessed by comparison with the beam propagation method (BPM). It is demonstrated that the coupled-mode theory (CMT) based on local modes is valid only for small tilt angles, whereas an improved formulation that takes into account the wavefront-tilt effect yields highly accurate results for relatively large tilt angles. The radiation loss at the input and the output junctions can also be estimated by a simple mode-matching method combined with the improved CMT. The coherent coupling between two junctions,which is neglected in the coupled-mode formulations, is observed in the BPM simulations.<>     

Transmission Properties of Fiber Probes

Transmission properties of tapered fiber including right cone fiber and bend optical fiber are discussed. The transmission efficiency of the tapered fiber is measured. The curve of transmission efficiency versus taper cone angle is given. By the scalar wave equation and Gaussian approximation, transmission properties of the two kinds of tapered fibers are analyzed, the power losses caused by taper cone angle and by the bending are also calculated. From the experiments and theoretical analysis, it could come to a conclusion that the wider the taper cone angle is,the higher the transmission efficiency will be.     

激光在锥形多模光纤中的耦合效率与传输模式

基于光线追迹的方法建立了典型锥形多模光纤的传输模型,结合激光干扰设备激光的特点,模拟计算了激光在锥形多模光纤中的耦合效率和传输模式,并设计进行了光学实验。仿真和实验结果表明:高斯激光光斑经锥形多模光纤传输后为圆环形光斑;耦合效率随激光入射角的增大而减小,减小的速率随入射角的增大而减小。为解决圆环形光斑分布,提出了将输出端连接的圆柱形光纤弯曲一定角度的方法,该方法可以将光斑改善为二维正态分布的光斑,理论耦合效率近80%。该研究为激光干扰设备的干扰激光直接介入激光制导武器对抗半实物仿真系统提供了理论和实验支持。     

Numerical analysis of integrated acoustooptic tunable filters withweighted coupling

A numerical approach based on the finite element method (FEM) and the beam propagation method (BPM) is newly formulated for design and modeling of integrated acoustooptic tunable filters (AOTF's) with weighted coupling on a piezoelectric substrate. First, acoustical field profiles in the substrate region and on the substrate surface are separately calculated with FEM and BPM, respectively. These two-dimensional (2-D) profiles are used for constructing three-dimensional (3-D) strain and electric field profiles. Then, from the strains and electric fields the refractive index changes due to acoustooptic (AO) and electrooptic (EO) effects are derived. Finally, by analyzing modified optical waveguides with AO8- and EO-induced changes in refractive indexes using again BPM, optical filter characteristics of AOTF's can be evaluated. Numerical examples are shown for AOTF's with a tapered acoustical directional coupler on a LiNbO₃ substrate     

锥形光纤的传输特性及其仿真研究

锥形光纤广泛应用于传光领域,它的传输特性已经成为研究热点。利用光线追迹法对锥形光纤的入射光线进行跟踪和分析,主要讨论了光从小端人大端出和从大端入小端出这两种情况。经过ZEMAX软件仿真和数值模拟得出：当光从小端入大端出时,锥形光纤的耦合效率迅速的提高,达到70％;当光从大端入端出时,出光端的光强随着小端的半径减小而增加...     

Tapered couplers for efficient interfacing between dielectric andphotonic crystal waveguides

We design tapered waveguide junctions for coupling between photonic crystal and traditional dielectric waveguides and evaluate their transmission efficiency. While the transmission efficiency is less than 60% using no taper, the tapered couplers have over 90% power transmission. We show that different types of couplers are needed for efficient coupling into and out of photonic crystal waveguides     

光纤型光可变衰减器的探索

通过熔融拉锥工艺制备熔锥光纤,将两熔锥光纤以一定的方式装配在二维精密微调架 上,制备光纤型光可变衰减器。利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤间的耦合,耦合效率决定了光能量的衰减程度,从而决定了光纤型光可变衰减器的性能。用耦合模理论分析了锥形光纤间的传输和耦合性质,并从实验上给出了两锥形光纤间的耦合与两锥形光纤间的距离的关系,为制备光纤型光可变衰减器提供了理论和实验依据。     

球聚焦型3×1光纤熔锥耦合器的研究

以线性耦合波方程为基础,采用散射矩阵的方法讨论了等三角分布的熔锥型3×1光纤耦合器,并用射线理论分析了球聚焦透镜光纤的端面效应。将未封装的3×3熔锥光纤耦合器在束腰处切断,并将锥端面熔成聚焦球端,利用光信号在光纤锥形区和球聚焦透镜中特有的传输和耦合特性,实现了光纤的耦合、连接和分束。结果表明:采用该方法耦合效率可达70%左右。同时大大增加了耦合系统的失调容差,降低了调试和封装的难度,因而有着广泛的实际应用价值。     

Wavelength characteristics of (2×2) optical channel-typedirectional couplers with symmetric or nonsymmetric coupling structures

The wavelength dependence of waveguide-type directional couplers is investigated with respect to waveguide pattern symmetry in the coupling region. A rough approximation of the dependence is determined based on simplified transfer matrix multiplications, followed by a more detailed computer calculation using the beam propagation method (BPM). Wavelength-flattened coupling characteristics over a wide range, for example, from 1.33-1.55 μm, are predicted for several types of directional coupler with waveguide width asymmetry or a tapered width structure in the coupling region     

基于温度变化的涂覆型熔锥光纤传输特性

基于光在熔锥光纤中传输的基本原理,分析了在外界温度不断变化的情况下涂覆折射率匹配液的熔锥光纤传输损耗特性。利用计算机仿真与实验得到了这种器件的传输损耗特性曲线,计算机仿真结果和实验结果的一致性很好地说明了熔锥光纤传输特性随温度变化的关系。随着外界环境温度的升高,折射率匹配液的折射率降低,熔锥光纤所携带的光功率占总光功率的比值增加,导致传输损耗减小。同时利用这种传输特性得到了一种温度可调的短通滤波器件,在一定温度下,这种滤波器对长波的滤波大于35dB,其滤波截止波长随温度升高而向长波方向漂移,温度系数是40nm/℃。     

Transient Analysis of Systems with Exponential Transmission Lines

Two computer solutions are given for pulse propagation along exponentially tapered transmission lines with arbitrary nonlinear sending and receiving networks. The solutions allow series and shunt loss terms per unit of length of the line. The method of characteristics is shown to be computationally superior to the cubic spline method in terms of accuracy and efficiency.     

高效率低旁瓣天线口面场分布函数研究

在赋形双反射面天线中,口面场分布函数对天线电气性能起到至关重要的作用。口面场分布函数妆接影响天线的增益和近角旁瓣。在传统卫星通信地面站中,要求天线第一旁瓣电平在-14dB以下,口面利用率在90%左右,而射电天文望远镜要求天线第一旁瓣电平小于-20dB,口面利用率要求在85%以上。研究并给出了一种整个口面能量均匀分布而外边缘低锥销的口面场分布函数,可以满足高增益,低旁瓣的要求。     

Transient analysis of coupled, tapered transmission lines witharbitrary nonlinear terminations

A fast and efficient method of simulating the time-domain transient response of coupled, tapered transmission lines is presented. A time-domain scattering parameter formulation is used to derive the simple closed-form expression for the voltage variables for uniform lossless lines; this expression is applied to tapered lines by dividing the lines into many uniform section. Computational efficiency and stability are achieved using recursive time-domain algorithms. When a quasi-TEM propagation mode is assumed, the method is applicable to nonlinear terminations and inhomogeneous dielectric media. Memory requirements are minimized and are independent of the number of time steps. Simulation results showed good agreement with experimental results     

一种基于SOI材料的新型可调谐光衰减器的设计

设计了一种新型的、基于SOI材料的可调谐光衰减器,其调制区采用了独特的双脊型PIN结构,增强了注入电流场与光场的重叠,提高电注入效率.用BPM方法分析了波导结构的传输损耗,用有限元法分析了二维PIN结的电注入特性.结果表明该结构的光衰减器有良好的性能.     

熔拉与腐蚀光纤探针传输特性的研究

用实验方法测量了用熔拉或腐蚀的方法制备的光纤探针的传输效率随光纤圆锥角的变化关系,作出传输效率曲线,通过测定光纤探针传输效率的实验,我们看到:在小锥角的情况下,用熔拉法制备的光纤探针与腐蚀的方法制备的光纤探针的传输效率基本相同。在大锥角的情况下,用腐蚀法制备的光纤探针传输效率高于熔拉的方法制备的光纤探针的传输效率。在锥角为50.4°时,腐蚀的光纤探针传输效率为78.8%,熔拉的光纤探针传输效率为76.6%。在相同的条件下,两者的传输效率的差别随入射光波长的增加而下降。     

Sidelobe levels of a large radio telescope employing a combination of physical and resistive tapering

The main beam, sidelobe levels, and effective collecting area of a proposed radio telescope array, operating at 12 MHz, are considered. The telescope consists of two large rectangular arrays containing several thousand half-wave dipoles arranged horizontally in a tee shape above a ground plane. A narrow beam is formed by cross-correlating the outputs of the individual arms of the tee. The possibility of sidelobe reduction using a form of physical tapering consisting of reducing the width of each rectangular arm at appropriate intervals along the array is assessed, by comparing the performance achieved with this type of taper to that obtainable with the more common resistive taper. It is concluded that when the effects of random errors in element excitation are considered the performance of the physically tapered and resistively tapered arrays compares favorably.