Active antenna array behavior

It has been recently demonstrated that arrays of coupled active antenna oscillating elements can be locked together by mutual radiation in order to form spatial power combining and beam steered arrays. In this paper a nonlinear coupled oscillator theory is developed which accounts for both the amplitude and phase behavior of an array of distributed coupled active antenna oscillators. In its canonical form the theory can be used to describe the behavior of any number of spatially displaced coupled elements placed in a chain. These elements can have unequal spacing and they can have arbitrary free-running oscillation frequencies. Unequal free-running amplitudes are also permitted. Experimental validation of the theory is presented for some basic cases in terms of frequency and amplitude variation under mutual injection locked conditions. In its particular form the theory developed is suited for use with recently reported active antenna imaging methods     

Analysis of coupled active waveguides: Comparison of different modeling techniques

A self consistent model for the analysis of phase locked array lasers is proposed and a comparison is made with the more frequently used coupled mode theory. It is shown that in most cases the coupled mode solutions are in good agreement with the self-consistent solution, but in some cases care should be taken in applying the coupled mode theory and an improvement of that theory may be useful.     

Mode analysis and stabilization of a spatial power combining arraywith strongly coupled oscillators

In order to attain stabilized power-combining operation of a strongly coupled active antenna array, a mode analysis for the multimoding array problem is presented, and an effective method for exciting only the in-phase power-combining mode is proposed. In a one-dimensional array of active antennas coupled mutually through microstrip lines, the frequencies and the voltage distributions of the normal modes are obtained. Stable modes of the array are identified using the averaged potential theory. Time evolutions of the mode amplitudes are also calculated. In order for only the desired power-combining mode to oscillate, appropriate resistors are introduced at the midpoints of the coupling lines between the active antennas. An experiment for arrays with up to eight active antennas has been carried using Gunn diodes. It has been confirmed that the introduction of the resistors is effective for stable excitation of the in-phase power-combining mode     

Approximate solution of eigenmode problems for layered coupled waveguide arrays

The characteristic modes of coupled waveguide arrays with a simple layered structure are examined using the approximate coupled wave theory. It is shown that evanescent waves may arise from total internal reflection at a boundary between two semi-infinite arrays. The transmission and reflection coefficients for this process are derived. If a suitable, finite, array is sandwiched between two semi-infinite arrays so that total internal reflection occurs at both boundaries, "guided" characteristic modes may arise. These have most of their power confined between the boundaries. The theory is used to specify an array distribution suitable for use in a transverse-mode-locked array laser.     

Higher order mode coupling effects in the feeding waveguide of a planar slot array

The effect of internal higher order modes in the feeding waveguide of a planar slot array is investigated. Both the centered-inclined coupling slot and the longitudinal-transverse coupling slot are considered. Method of moments solutions to pertinent coupled integral equations are investigated for arrays of coupling slots of the centered-inclined and longitudinal-transverse types between a main waveguide and crossed branch waveguides. It is demonstrated that, by including the TE/sub 20/ mode coupling in the analysis, most of the higher order mode effects can be accounted for in reduced height waveguides, whereas in waveguides of standard height there may be a small additional effect arising from the TE/sub 01/ mode coupling.<>     

基于耦合本振阵列的旁瓣抑制技术研究

以耦合振荡器阵列作为本振阵列,提出具有旁瓣抑制的接收波束天线阵列扩展结构,推导了其接收波束形成的方向图函数,分析了该接收波束旁瓣抑制技术的可行性,并通过计算机仿真验证了旁瓣抑制技术的理论分析结果,为耦合振荡器阵列应用于天线接收的干扰抑制技术提供了理论基础。     

Transverse mode control and switching in gas laser arrays

Theoretical and experimental investigations of multiple transverse mode laser oscillation involving spatially varying gain and loss are carried out. The effect of gain and loss distribution on mode competition is analyzed. Numerical examples are given for a CO₂ waveguide laser array. Experimental results of CO₂ laser arrays are found to be consistent with the theory, and robust in-phase coupled mode array operation has been achieved     

Critères généraux de conception des réseaux de diodes lasers à rubans couplés par champs évanescents

The aim of this article is to define the general criteria for design of phase-locked diode laser arrays. A general method for designing these devices is presented using the effective index method and the coupled mode theory. The confinement required for the individual diodes is defined, and the allowed structure geometries are determined.     

Active antenna array lumped ring configuration

Coupled active antenna oscillator arrays are used for power-combining at microwave and millimeter-wave frequencies. It is known that the relative phase determined by the element separation distance ultimately determines the array operational mode and, hence, far-field radiation characteristics. Separately, it is known that coupled oscillator modal stability is achieved by coupling oscillators through lumped capacitive elements. In this paper, an arrangement whereby lumped capacitive elements (placed across the oscillator loads) and radiative coupling are employed concurrently is investigated. The arrangement takes the form of a ring of coupled oscillators used to excite a 2×2 antenna array. The effect that these couplings have on array behavior are evaluated using time-domain analysis and analytically derived equations. Experimental results for far-field radiation patterns are discussed in relation to coupled oscillator dynamical behavior. These suggest that the theoretical predictions are valid, offering a robust design tool for studies of larger power-combining arrays     

Measurement and modelling of radiative coupling in oscillatorarrays

Arrays of coupled oscillators can be used for power-combining at microwave and millimeter-wave frequencies, and have been successfully demonstrated with a variety of devices. Such arrays have also recently been mode-locked for pulse generation, and can be configured for phase-shifterless beam scanning. The nonlinear theory of coupled oscillator phase dynamics depends crucially on the parameters describing the coupled between oscillators. Methods for experimental characterization of these parameters are described here, and simple models which reproduce the measurements quite well are developed. The models apply to radiative coupling and the effects of external reflectors which are sometimes used for stabilization. The theory is verified with a two-oscillator system     

Nonlinear analysis of phase relationships in quasi-opticaloscillator arrays

A dynamic theory of coupled oscillators is developed and applied to the class of loosely coupled quasi-optical oscillator arrays. This theory permits the calculation of stable, steady-state phase relationships between the oscillators. The distribution of free-running frequencies and the coupling parameters are most important in determining the behavior of the arrays. It is found that free-running frequencies of the peripheral elements have the strongest influence on the steady-state phase relationships. The influence of randomness in the frequency distribution is considered for the case of broadside beamforming, establishing a critical value for the coupling strength in order to maintain mutual synchronization with a specified maximum beam deviation. Techniques for simplifying the calculation of phase relationships for some common coupling parameters are also developed     

?Excess? modes in gain-guided laser arrays

It is demonstrated that the number of modes in an array of gain-guided lasers can exceed the number of elements even when each element only supports one mode. Therefore the number of array modes cannot be found using coupled-mode theory. This has implications for the design and analysis of gain-guided arrays.     

Traveling Waves in Coupled Yagi Structures

The propagating mode in a coupled Yagi-Uda array of cylindrical wires is studied. The current distribution in each element, the phase velocity; and the cutoff frequency of the propagating mode are found, firstly by a numerical method and secondly by a method based on an assumed current distribution. These two methods yield essentially the same results. Mutual coupling between the arrays is studied. The characteristics of the propagating waves in the coupled Yagi-Uda structure have been measured. The experimental K-beta diagram of the waves is obtained and is found to be in good agreement with the theory.     

Eigenmodes of a periodic array of coupled waveguides

General properties of eigenmodes in periodic arrays of coupled waveguides are considered. The Floquet channel model is used to analyze arrays operating in the quasi-periodic mode. Relationships for the orthogonality of different types of eigenmodes are obtained on the basis of the Lorentz lemma and the active power theorem. The problem of excitation of array eigenmodes by given currents is solved. The relation between two representations of the array field, by means of the eigenmode expansion and in the form of the Fourier integral, is shown by the example of an array of coupled slot lines.     

弯曲光纤布拉格光栅光谱特性的研究

从理论与实验两方面研究了基于普通单模光纤的光纤布拉格光栅在弯曲时光谱特性的变化。基于耦合模理论, 以弯曲光纤为参考波导, 研究了弯曲波导的分析模型和漏模求解工具, 考虑了弯曲时光弹效应的影响, 得到弯曲光纤中的准导模（漏模）; 分析了弯曲情况下, 布拉格波长的变化情况, 与实验结果基本吻合。在1 cm的弯曲半径下, 布拉格波长向长波长的偏移在10-2nm量级。     

均匀分布锁相列阵半导体激光器的微扰理论

本文从宽接触半导体激光器的简单模型出发,运用微扰理论分析了均匀分布锁相列阵半导体激光器的侧模行为。分析表明,对增益导引、折射率导引锁相列阵,器件一般以N阶模工作,但在增益导引列阵中将会出现大于N的高阶模。反折射率导引均匀分布锁相列阵可获得基侧模工作,其远场由于周期性微扰的作用表现为三瓣,能量主要集中于中心瓣上。     

Design and modeling of passive optical switches and power dividersusing non-planar coupled fiber arrays

Arrays of coupled waveguides such as the ubiquitous directional coupler are used extensively in optoelectronic devices, with demonstrated applications to optical communications networks, fiber interferometers, and optical homodyne receivers. In order to analyze the transmission characteristics of circular arrays of coupled optical fibers, we have developed a matrix representation of the coupled-mode formalism, allowing for varying fiber diameters and differing coupling strengths between the fibers in the array. The model is used to identify design criteria for application of such arrays as passive optical switches and power dividers     

耦合本振阵列的旁瓣抑制技术研究

论文以耦合振荡器阵列作为本振阵列,提出天线阵列接收波束具有旁瓣抑制的扩展结构,推导了其接收波束形成的方向图函数,分析了该接收波束旁瓣抑制技术的可行性,并通过计算机仿真验证了旁瓣抑制技术的理论分析结果,为耦合振荡器阵列在接收技术上的应用提供了理论基础。     

超结构光纤Bragg光栅制作模型及其耦合模理论

从衍射光学角度出发，分析了超结构光纤Bragg光栅（SFBG）的制作理论模型，进而采用理想模展开的耦合模理论对SFBG的模场分布进行了分析，给出了SFBG的耦合模方程，并采用数值计算方法对其反射谱进行了计算机模拟。     

Towards a Better Prediction of Cell Settling on Nanostructure Arrays—Simple Means to Complicated Ends

Vertical arrays of nanostructures (NSs) are emerging as promising platforms for probing and manipulating live mammalian cells. The broad range of applications requires different types of interfaces, but cell settling on NS arrays is not yet fully controlled and understood. Cells are both seen to deform completely into NS arrays and to stay suspended like tiny fakirs, which have hitherto been explained with differences in NS spacing or density. Here, a better understanding of this phenomenon is provided by using a model that takes into account the extreme membrane deformation needed for a cell to settle into a NS array. It is shown that, in addition to the NS density, cell settling depends strongly on the dimensions of the single NS, and that the settling can be predicted for a given NS array geometry. The predictive power of the model is confirmed by experiments and good agreement with cases from the literature. Furthermore, the influence of cell‐related parameters is evaluated theoretically and a generic method of tuning cell settling through surface coating is demonstrated experimentally. These findings allow a more rational design of NS arrays for the numerous exciting biological applications where the mode of cell settling is crucial.