Vibration frequency of a fused biconical taper (FBT) lightwavecoupler

A simple formula for the assessment of the lowest frequency of free lateral vibrations of fused biconical taper (FBT) lightwave coupler, subjected to initial tensile strain (force), is proposed. This formula can be used to determine the initial tensile strain that would result in a sufficiently high vibration frequency and at the same time would be acceptable from the standpoint of the long-term reliability of the material. The obtained formula can be applied also for the evaluation of the initial tensile force, stress and strain from the measured frequency of vibrations     

Circular-disk microstrip antenna with an air gap

The circular-disk microstrip antenna with an air gap between the substrate and the ground plane is analyzed using the cavity-model theory. A simple formula for the resonant frequencies is obtained. The internal fields, the radiation fields, the effective loss tangent, and the input impedance are derived when the antenna is provided with a coaxial feed. The theory predicts that the air gap does not alter the relative field patterns significantly but it provides a simple parameter by which the resonant frequencies of the antenna can be tuned. Measurements have been performed on a 5 cm circular-disk microstrip antenna with an air gap and good agreement between theory and experiment is obtained.     

An analytic method for designing passband flattened DWDM demultiplexers using spatial phase modulation

An analytic method of spatial phase modulation based on Fourier analysis is introduced for the design of a planar waveguide demultiplexer with a flat-top spectral response. An analytic formula for an etched diffraction grating demultiplexer is derived using the scalar diffraction theory. The spatial phase modulation is realized by slightly adjusting each grating facet's position according to the analytic formula to obtain a spectral response with a flat top and sharp transitions as well as a good dispersion characteristic. The analytic formula is characterized by two parameters: a transverse shift distance and a profile exponent for the phase modulation. A linear relation between the passband width and the transverse shift distance is given, and an optimal figure of merit of the spectral response is obtained by choosing an appropriate profile exponent. A numerical example of a typical SiO/sub 2/ etched diffraction grating demultiplexer is used to demonstrate the advantages of this method.     

复口径Kirchhoff褶积公式和孔径辐射的复射线束仿真

本文基于解析延拓的概念,由实口径的Kirchhoff褶积公式导出了复口径的Kirchhoff褶积公式。理论分析和数值计算表明,利用复口径Kirchhoff褶积公式可以实现对孔径辐射场的复射线束仿真,从而为进一步研究孔径辐射场在复杂媒质中的传播提供了一种新方法。     

Propagation constants of guided modes in graded-index fibre with polynomial-profile core

Corrected propagation of the guided modes in a graded-index fibre with a polynomial-profile core are given in analytic form by using a modified Maslov's formula. The result coincides with one obtained by the evanescent-field theory.     

A Method for the Calculation of the Radiation-Pattern and Mode-Conversion Properties of a Solid-State Heterojunction Laser

A solution of the laser fields, both inside and outside the laser, is given in terms of the mode-conversion coefficients and an integral equation for the radiation pattern. It is shown how very accurate analytic solutions can be obtained by what, at first sight, appear to be extremely crude approximations. The reason is that mode conversion is taken implicitly into account by using a multiplier, whose exact form does not appear to be very critical, as a weighting function to average two different formulas for the function representing the radiation; and with the correct form for it, all the mode-conversion and reflection coefficients can be legitimately ignored. A plane-wave formula for this multiplier is a good first approximation, and a number of existing expressions occurring in the literature are obtained in this way. It is also shown rigorously that the results of an earlier obliquity-factor analysis apply. Further refinements are introduced to allow for higher order discrete modes, and good approximate analytic forms for the mode-reflection and conversion coefficients are obtained. A check with a rather extreme example shows excellent agreement with Ikegami's numerical computation for the dominant-mode reflection at the laser-air interface. The methods of this paper are applicable to general laser structures of cylindrical geometry with either continuous or discontinuous variations in refractive index. Very accurate numerical solutions should be obtainable after only one iteration of the integral equation, starting with the reflection-modified form of Hockham's formula as initiating function.     

光折变晶体中双光束耦合时间响应特性的研究

从描述双光束耦合规律的动态方程组出发．在考虑了光栅调制度变化后，给出了包含晶体固有参数、入射总光强、入射夹角、光强比等变量在内的写入响应时间解析表达式，实验结果与理论分析定性符合很好。     

辐照条件下石英光纤的损耗理论

本文提出了一种计算石英光纤辐照损伤的理论,特点是通过在实验室中测出的来推算太空中卫星所用石英光纤中的辐照抽伤情况,而解决了以往在实验室里难以模拟太空环境而造成石英光纤辐照损耗难以推算的困难,并且该理论亦可应用到其它的在辐照环境中工作的石英光纤。     

Birefringence in bent single-mode fibers

Changes to field properties when an optical fiber is bent are considered. A formula is obtained for the geometrical birefringence in a single-mode fiber due to bending, and is explicitly evaluated for a Gaussian field approximation, giving a simple analytic expression; it is also evaluated for more exact fields. Scalar theory is not sufficient to describe this birefringence, as reported previously, and vector or polarization corrections must be included in the theory. This birefringence is several orders of magnitude less than stress-induced bending birefringence     

Complex source representation of time harmonic radiation from aplane aperture

Developed here is a new complex source representation for time harmonic radiation from a plane aperture which is the Kirchhoff's spatial convolution formula of a complex plane aperture with the complex aperture field being the analytic extension of the original aperture field. A systematic study for a one-dimensional linearly phased cosine aperture distribution confirms the effectiveness of the new method in the simulation of the time harmonic radiation     

Fluorinated and Alkylthiolated Polymeric Donors Enable both Efficient Fullerene and Nonfullerene Polymer Solar Cells

In this work, four donor (D)–acceptor (A) copolymers based on benzodithiophene (BDT) and benzothiadiazole (BT) with different alkylthiolated and/or fluorinated side chains are developed for efficient fullerene and nonfullerene polymer solar cells (PSCs). The synergistic effect of sulfuration and fluorination on the optical absorption, energy level, crystallinity, carrier mobility, blend morphology, and photovoltaic performance is investigated systematically. By incorporating sulfur atoms onto the side chains, a little blueshifted but significantly increased absorption can be obtained for PBDTS‐FBT compared to PBDT‐FBT . On the other side, a little more blueshifted but much stronger absorption and much lower‐lying highest occupied molecular orbital (HOMO) level can be realized for PBDTF‐FBT when introducing fluorine atoms instead of sulfur atoms. With the combination of both fluorination and sulfuration strategies, PBDTS‐FBT exhibits the best absorption ability, lowest HOMO energy level, and highest crystallinity, which make PBDTSF‐FBT devices show the highest power conversion efficiency (PCE) of 10.69% in fullerene PSCs and 11.66% in nonfullerene PSCs. The PCE of 11.66% is the best value for PSCs based on BT‐containing copolymer donors reported so far. The results indicate that fluorination and sulfuration have a synergistically positive effect on the performance of D–A photovoltaic copolymers and their solar cell devices.     

Phase-locked arrays of antiguides: analytical theory

By employing a variational technique on the eigenvalue equation for finite arrays of antiguides we obtain accurate analytical expressions for key parameters characterizing the resonant array modes: the radiation loss at resonance, α_RR, and the propagation constant at resonance. The previously empirical finding that α_RR is equal to the radiation loss of a single antiguide divided by the number of array elements is found to be a good approximation only for large element/interelement width ratios (⩾3) and for, high-index-step (Δn⩾0.05) devices. By using an expansion, the radiation loss versus index-step curve is well approximated near resonance by a parabola, which gives curve halfwidths at half intensity only 10 to 15% less than numerically calculated values. An extremely accurate approximation formula is obtained for the resonant-mode propagation constant over large ranges in index-step variation around the resonance point. The obtained formulae are discussed in light of device design     

The impedance of a short dipole antenna in a magnetoplasma

A formula for the impedance of a short cylindrical dipole in a magnetoplasma is derived using quasi-static electromagnetic theory. The formula is valid in a lossy plasma and for any dipole orientation with respect to the magnetic field. The dipole impedance is found to have a positive real part under lossless conditions when the quasi-static differential equation is hyperbolic; this indicates that the quasi-static theory predicts a form of radiation. It is shown that the quasi-static theory can be interpreted in terms of scaled coordinates and that a cylindrical dipole in a magnetoplasma has a free space equivalent with a distorted shape. A conductance correction term obtained from Langmuir probe theory is shown to be significant. Laboratory measurements of monopole impedance are compared with the theoretical calculations.     

Microbending loss in monomode fibres

A simple analytic formula for the microbending loss in monomode fibres of arbitrary refractive-index profile is presented. This loss essentially depends on the spot size of the fundamental fibre mode only. Therefore W-fibres, for example, are as sensitive to microbending as conventional cladded-core fibres.     

Calculation of Radiation from a Helically Cut Waveguide for a Gyrotron Mode Converter in the Quasi-Optical Approximation

We present results of calculations of the radiation from a helically cut waveguide launcher, a so-called Vlasov launcher, which is commonly used either internal or external to a gyrotron for purposes of mode conversion. A gyrotron internal mode converter consists of such a launcher that radiates the waveguide mode as a nearly Gaussian beam in free space followed by a set of mirrors to focus and direct the radiation. The radiation from the launcher is first calculated using a geometric optics representation of the waveguide mode. Then the radiation is calculated in the quasi-optical limit, including diffraction. These analytic results are compared to a rigorous calculation using the computer code SURF3D, which uses an electric field integral equation (EFIE) approach. Good agreement is obtained between the quasi-optical theory and the SURF3D calculation. The present results provide new insights into the accuracy of the quasi-optical theory and may be useful for the design and improvement of Vlasov-type mode converters.     

探测器温度对非致冷型微测辐射热计热像仪测温的影响与修正

根据红外辐射理论和红外热像仪的测温原理,得到了红外热像仪测温的计算公式及测温程序,分析了非致冷微测辐射热计的温度对测温的影响,并得出了相应的修正公式和修正方法.得到的两种修正方法简单易行,为非致冷微测辐射热计阵列热像仪的设计制造及实际使用提供了一定的方法和依据.     

球面近远场和远近场变换算法

天线的远场对于研究天线辐射特性具有重大意义，近场测量技术因其能够避免直接测量远场而得到广泛应用，该技术采用近远场变换获得远场，然而，检验该远场的准确性也是很重要的.为了解决此类问题，文中以球面近场测量为例，提供了一种解决方案.该方案主要探讨了球面波模式展开理论，该理论是实现球面近远场变换算法的关键，其将待测天线在空间建立的场展开成球面波函数之和，天线的加权系数既包含了远场信息也包含了近场信息.因此，不仅能够利用近场测量信息获得远场辐射特性，同样能够利用远场辐射特性反推得到近场处电场，这样就能检验由近远场变换算法得到的远场是否准确.文中首先推算得到了近远场变换公式，随后进一步推算得到远近场变换的公式，最后将本文算法计算结果与FEKO测量结果进行比较，二者吻合良好，从而证实了本文两种算法的有效性.     

980/1 550保偏光纤波分复用器

从耦合模理论出发,分析了980／1550熔融拉锥（FBT）型保偏光纤（PMF）波分复用器（WDM）的工作原理,设计了WDM的制作方法。在FBT台上,通过控制火焰的温度和宽度以及拉伸速度,有效控制WDM的拉伸长度和耦合区结构,用1550nm的PMF和H11060单模光纤（SMF）成功研制了高性能的980／1550PMFWDM。测试结果表明：在1550nm波长上,该WDM具有0．2dB的插入损耗、32dB的隔离度和22．8dB的消光比偏振特性;在980nm波长上,具有0．2dB的插入损耗、14_8dB的隔离度。该器件除了具有SMFWDM的特性外,1550nm端口还具有偏振保持特性,它将促进PMF激光器和放大器快速发展。     

Two Regioisomeric π‐Conjugated Small Molecules: Synthesis,Photophysical, Packing,and Optoelectronic Properties

Two regioisomeric D₁‐A‐D‐A‐D₁ type π‐conjugated molecules (1,4‐bis{5‐[4‐(5‐fluoro‐7‐(5‐hexylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole)]­thiophen‐2‐yl}‐2,5‐bis(hexyldecyloxy)benzene (Prox‐FBT) and 1,4‐bis{5‐[4‐(6‐fluoro‐7‐(5‐hexylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole)]­thiophen‐2‐yl}‐2,5‐bis(hexyldecyloxy)benzene (Dis‐FBT)) are synthesized, by controlling the fluorine topology to be proximal or distal relative to the central core. The different F geometries are confirmed by the ¹H–¹H nuclear Overhauer effect spectroscopy (NOESY). Clearly different optical, electrochemical, and thermal transition behaviors are obtained, i.e., stronger absorption, deeper valance band (by ≈0.2 eV), and higher melting/recrystallization temperatures (by 7–20 °C) are observed for Dis‐FBT. The different intermolecular packing and unit cell structures are also calculated for the two regioisomers, based on the powder X‐ray diffraction and 2D grazing‐incidence wide‐angle X‐ray diffraction measurements. A tighter π–π packing with a preferential monoclinic face‐on orientation is extracted for Dis‐FBT, compared to Prox‐FBT with bimodal orientations. Different topological structures significantly affect the electrical and photovoltaic properties, where Prox‐FBT shows higher parallel hole mobility (2.3 × 10^?3 cm² V^?1 s^?1), but Dis‐FBT demonstrates higher power conversion efficiency (5.47%) with a larger open‐circuit voltage of 0.95 V (vs 0.79 V for Prox‐FBT). The findings suggest that small changes in the topological geometry can affect the electronic structure as well as self‐assembly behaviors, which can possibly be utilized for fine‐adjusting the electrical properties and further optimization of optoelectronic devices.     

一种新的光缆窃听系统研究

基于光纤弯曲辐射,提出了四步光缆窃听法,即"剥光缆,弯光纤,取信号,解信息"。通过推导光纤弯曲损耗公式和考察两类窃听影响因素,得出隐蔽窃听所需的光纤弯曲最佳曲率半径值。在此理论指导下,设计了窃听系统框架结构,并搭建了光纤窃听实验系统。经理论和实验证明:四步光缆窃听法具有可行性,且隐蔽性好、检测难度大。