Guided electromagnetic waves in a periodically nonuniform tunnel

A boundary value analysis is outlined for the transmission in a circular tunnel that contains a thin axial conductor. The series impedance of the latter is allowed to vary in a periodic fashion throughout its length. Simplifications of the formal mode equation are achieved by invoking quasi-static conditions used in previous studies. It is shown that the axial nonuniformity can be represented approximately as a modification of the series impedance of the equivalent transmission line of the composite tunnel structure.     

Generalised patterns of nonuniformity for solvable algebraic and transcendental transmission lines

The aim of this letter is to show that, on transforming the independent variable x of the telegrapher's equation for nonuniform lines to another independent variable w=F(x) which is some function of the distance variable x, and then constraining the transformed equation, so obtained, to represent either Su's trigonometric or his hyperbolic line, a generalised pattern of nonuniformity, expressible either in terms of any arbitrary w=F(x), or in terms of another arbitrary f(x) [where f(x)=Z(x)/Z0, Z0 being an impedance constant, defines the distribution of nonuniformity for the series impedance Z(x) per unit length] may be obtained. In addition, the generalised expressions for the distributions of nonuniformity for a prototype of Cheby?shev line are derived, and it is shown that the Cheby?shev line is a subclass of Hellstrom's generalised proportional line.     

Effects of the spatial nonuniformity of optical transverse modes on the modulation response of vertical-cavity surface-emitting lasers

We present detailed numerical simulations to clarify the important role that the nonuniformity of the transverse optical mode plays for the high-speed response of oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The comprehensive laser diode simulator, Minilase, as well as a one-dimensional rate equation model are used as simulation tools. It is demonstrated that, due to the nonuniform optical intensity, carriers at different locations in the quantum well have different stimulated recombination rates, and therefore exhibit different dynamic responses to small signal modulation. This nonuniformity causes an overdamping of the relaxation oscillation, as well as a low-frequency roll-off of the modulation response. Due to this nonlinear effect, the intrinsic maximum bandwidth of VCSELs with oxide confined apertures is shown to be much smaller than predicted by the conventional rate equation model which assumes uniform optical intensity. We further demonstrate that this damping effect can be greatly reduced by restricting the current injection to be well within the transverse optical field. This is achievable by using tapered oxides to make the electrical aperture smaller than the optical aperture, which thereby improves the modulation bandwidth significantly.     

Nonlinear dynamics of femtosecond optical solitary wave propagationat the zero dispersion point

A perturbed nonlinear Schrodinger equation, describing nonlinear pulse propagation of femtosecond duration in optical fibers at the zero dispersion point, is considered. This equation is reduced to an ordinary differential equation, which is treated by means of Hamiltonian dynamics techniques. Conditions for solitary wave formation, as well as the solutions themselves, namely, a bright soliton, a rarefaction soliton, and a pair of dark solitons, are derived analytically. The shifts of the solitary wave velocity, the angular frequency, and the wavenumber, as well as the peak power required to launch a bright soliton are also obtained. The connection among the point initial conditions of the pulse and the type of solitary wave that can be excited is finally presented     

Propagation on a Cylindrical Surface Wave Structure Having Radially Nonuniform Dielectric

The possibility that a radially nonuniform dielectric might enhance the propagation characteristics of a surface wave line is discussed in terms of the axial cylindrical surface wave on a cylindrical structure. Attention is given to the field structure in the dielectric to determine the effect of the nonuniformity on the dielectric loss. Conclusions are deferred, however, until the change in surface impedance is also examined, since it essentially determines conductor loss and decay coefficient. The surface impedance is examined using the radial transmission line formalism of Marcuvitz. The modified field structure in the nonuniform dielectric and the concomitant change in dielectric loss is found to be most important for the surface wave structure; the nonuniformity changes the surface impedance only slightly since it is already highly reactive.     

基于PDE去鬼影的自适应非均匀性校正算法研究

针对基于场景的自适应校正算法普遍存在鬼影的问题, 分析了神经网络算法(NN-NUC)产生鬼影的原因,并在此基础上提出了用基于偏微分方程(PDE)的非线性滤波方法取代NN-NUC算法中邻域平均的方法来获取期望图像,从而减少边缘像素误差,达到消除鬼影的目的.采用实际采集的红外图像进行实验,结果表明,很好地消除了鬼影.与已有的几种去鬼影的方法相比,具有更快的收敛性.     

红外焦平面阵列器件非均匀性分析

红外焦平面阵列固有的非均匀性严重地制约着其成像系统的成像质量,必须对其进行补偿校正。在深入地研究了非均匀性的各种来源及其表现形式的基础上,论述了校正原理,并提出了一种普遍适用的测量方法。     

负双轴晶体光轴角和光线轴角推导的新方法

为了有助于人们更好的理解和区分双轴晶体的光轴角和光线轴角,以及对光在晶体中传播的理解,本文以负双轴晶体为例,根据光轴和光线轴的定义,从菲涅耳波面法线方程和光线方程出发,推导出了光轴角和光线轴角的表达式。作为对此新方法的验证,通过几何作图法得到了一致的结果,由此证明这一新方法是正确的。     

Evaluating the effect of photogeneration nonuniformity on the accuracy of laser simulation of the transient radiation response in semiconductor devices and circuits

The effect is investigated of photogeneration nonuniformity, both vertical and horizontal, on the accuracy of laser simulation of the transient radiation response (dose-rate effects) in silicon devices and circuits. It is shown that vertical nonuniformity, due to optical absorption by the substrate, has an insignificant effect if the wavelength is selected to be 1.06–1.08 μm, the first harmonic of a Nd laser. Horizontal nonuniformity, due to the metallization pattern, is shown to disappear on a timescale comparable with the laser pulse width for most practical ICs, as a result of lateral flow of excess carriers by diffusion and drift. When this is the case, the influence of the metallization pattern is found to be fully determined by the area of metallization relative to the over-all chip area. Using a diffuser of laser radiation is proposed as a way to reduce this effect. An optical model is developed to calculate equivalent dose for the diffuse radiation. It is demonstrated that this approach indeed alleviates the horizontal nonuniformity of equivalent dose rate related to the metallization pattern. The predictions are verified by experiment.     

利用FPGA实现红外焦平面器件的非均匀性校正

与红外单元器件系统相比,焦平面面阵测器的一个最大的缺点是其固有的非均匀性,尽管现在面阵探测器的非均匀性有了很大改进,但是非均匀性仍然限制凝视红色系统的探测性能。实用化、、实时的非均匀性校正是红外焦平面器件应用的一个关键技术,尽管现在已经有很多种基于场景的非均匀性校正方法,但是两点校正算法仍然是基础的校正方法,有不可替代的价值。两点校正算法的流程简单固定,非常适合用ＦＰＧＡ实现。文章介绍了利用ＦＰＧ     

变系数组合KdV方程的新的孤立波解

在辅助方程法的基础上,给出辅助方程和函数变换相结合的一种方法,并借助符号计算系统Math-ematica,获得了变系数组合KdV方程的新的孤立波解和三角函数解.这种方法在寻找其它变系数非线性发展方程的新的孤立波解和三角函数解方面具有普遍意义.     

On the validity of estimating axial nonuniformity of photon density from output power ratio in uniform grating DFB lasers

The validity of the method of estimating nonuniformity in axial photon distribution from front-to-rear output power ratio has been studied by an effective index transfer matrix method. The correlation between the front-to-rear output power ratio and the maximum-to-minimum photon density ratio is shown to be good over the whole useful range of the grating coupling coefficient in uniform grating DFB laser with low-reflection/high-reflection facets, and an accurate estimation is possible. However, the correlation becomes poor as the reflectivity of the high-reflection facet decreases and the coupling coefficient increases, resulting in poor estimation.     

一种基于定标的红外图像非均匀性分区域校正算法

红外探测器的非均匀性问题直接影响红外成像质量和测量精度。地基红外辐射测量系统对远距离飞行目标进行成像时往往不能占满全靶面区域。为提高图像质量,提出了一种基于定标的非均匀性分区域校正算法。以靶面大小为640×512的制冷型中波红外探测器为实验对象,基于黑体定标的两点校正法,采用全靶面校正算法及本文算法进行了验证。结果表明,当成像区域小于全靶面的1/3时,分区域非均匀性校正后非均匀性误差低于0.002%。与全靶面非均匀性校正算法相比,此校正算法使非均匀度进一步降低了30%至75%不等,非均匀性误差的下降率大于30%。采用本文算法后,各区域的非均匀度进一步下降,校正目视效果进一步提高。因此该校正方法具有一定的工程应用价值。     

场景统计类红外图像非均匀性校正算法研究

场景统计类非均匀性校正算法对场景分布进行假定,获得探测单元接收红外能量的一、二阶矩,进而估计探测单元的响应参数,校正非均匀性。分析比较了现有的场景统计类非均匀性校正算法,并应用交互多模(IMM)算法校正非均匀性,实验结果表明以连续图像序列作为观测数据时,能够有效地校正非均匀性,扩展了卡尔曼滤波法的适用范围。对各种方法进行仿真,表明删算法具有较好的收敛特性。     

多CCD拼接相机中图像传感器不均匀性校正

CCD图像传感器不均匀特性是影响光电测量设备精度的一个重要因素.在分析了单片CCD图像传感器不均匀特性基础上,提出了多CCD拼接相机系统中不均匀特性的校正方法.大量实验结果表明,利用该校正方法不仅保持原图像的目标,而且简单快速,具有通用性,能够显著提高系统测量精度.该方法可行且对其他光电测量设备有参考意义.     

红外焦平面非均匀性噪声的空间频率特性及空间自适应非均匀性校正方法改进

分析了红外焦平面阵列非均匀性噪声的空间频率特性,指出空间低频噪声为其中的主要成分．利用实际IRF—PA定标数据,也得出了相同结论．针对传统空域自适应校正方法去除低频空间噪声存在的不足,本文提出采用一点校正和空域自适应校正相结合的方法．实验结果表明,新方法在空间低频噪声占优时能获得好的校正效果．     

1024元MCT红外焦平面线列等角度扫描成像系统

文章介绍了一种带读出电路的１０２４元短波ＭＣＴ红外等角度扫描成像系统．叙述了该扫描成像系统的构成,在图像处理中应注意的两个主要问题:探测器非均匀性校正和行列图像信号的修正．该扫描成像系统采用国产１０２４元线列ＭＣＴ(碲镉汞)焦平面器件,自行研制的同轴透射式光学系统和一维等角度并行扫描方式,扫描效率超过８８%,扫描半周期为５秒,每帧像素为１０２４×１６００．该系统在野外获得了较为理想的红外图像．     

有振幅调制光束经锯齿光阑的衍射特性

用惠更斯-菲涅耳衍射积分对有振幅调制光束经锯齿光阑的衍射作了研究,并与经圆孔硬边光阑的衍射作了计算比较.另外讨论了锯齿光阑参数对有振幅调制光束衍射特性的影响.结果表明,锯齿光阑有较大的填充因子,能抑制轴上光强的衍射调制,并降低横向光强分布的不均匀性.     

Concentration profile calculation for buried ion-exchanged channelwaveguides in glass using explicit space-charge analysis

Ionic conductivity inhomogeneity and its relation to space charge is analyzed in the case of a two-ion exchange for channel waveguide fabrication in optical glass. The space-charge evolution equation is derived and discussed in a general binary ion exchange context. This leads to an efficient algorithm which computes current-density nonuniformity in the field-assisted burying of ion-exchanged waveguides. The algorithm exhibits excellent agreement with the classic potential equation perturbed by nonhomogeneous ionic conductivity, and is appreciably faster. We show that the homogeneous current-density assumption is inaccurate for the calculation of the burying depth and waveguide size in the case of a realistic glass with nonlinear ionic diffusivity     

基于定标的红外焦平面非均匀性校正算法研究

红外焦平面阵列普遍存在非均匀性,这会严重影响其成像质量。基于定标的非均匀性校正算法因其易于硬件实现,在工程应用中已被广泛采用。本文介绍了近年来基于定标的非均匀性校正算法的研究进展,对各种算法的优势及缺点进行了对比,并针对算法特点和工程需求做出了相应的分析。