多波导阵列耦合研究

提出了一种求解波导阵列耦合特性的方法.采用拉普拉斯变换,将同时考虑相邻和次相邻波导耦合作用的波导阵列耦合模方程组变为一个线性方程组,利用矩阵的LU分解法(将系数矩阵分解为单位下三角阵L与上三角阵U的乘积)求出该线性方程组的解.然后根据给定的初始条件进行拉普拉斯变换反演,求出耦合模方程组的解.采用该方法研究了五波导阵列,光从中间一个波导入射和从五个波导入射时的耦合特性,给出了每个波导中光功率变化规律曲线,并将所得结果与同样条件下仅考虑相邻波导耦合的结果做了比较.采用该方法可以求出任意数目波导组成的阵列,考虑任意波导之间耦合的耦合模方程组的解.     

Intensity dynamics in a waveguide array laser

We consider experimentally and theoretically the optical field dynamics of a five-emitter laser array subject to a ramped injection current. We have achieved experimentally an array that produces a robust oscillatory power output with a nearly constant π phase shift between the oscillations from each waveguide. The output power also decreases linearly as a function of waveguide number. Those behaviors persisted for pump currents varying between 380 and 500 mA with only a slight change in phase. Of note is the fact that the fundamental frequency of oscillation increases with injection current, and higher harmonics are produced above a threshold current of approximately 380 mA. Experimental observations and theoretical predictions are in agreement. A low dimensional model was also developed and the impact of the nonuniform injection current studied. A nonuniform injection current is capable of shifting the bifurcations of the waveguide array providing a valuable method of array tuning without additional gain or structural alterations to the array.     

Semi-Analytical Simulation of Titanium-Indiffused Lithium Niobate–Integrated Optic Directional Couplers Consisting of Curved Waveguides

Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO ₃ curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple.     

高功率平板波导螺旋阵列天线设计

提出了一种工作在C波段的高功率平板波导螺旋阵列天线。以平板波导馈电,降低了馈电复杂性和馈电结构高度;对基本的电探针结构进行改进,通过控制扇形缝隙的圆心角大小来调整耦合量,并采用上下脊结构消除反射;设计了短螺旋天线结构,通过分离的参数分别优化轴比和反射,得到天线的轴比在?7°～7°的范围内小于0.5 dB;构建了一个20单元的直线馈电阵列,通过电探针结构从平板波导中耦合能量,实现了20单元的等幅馈电。最后仿真了一个工作在4.3 GHz,包含20×20个单元的螺旋阵列天线,结果表明:该天线的增益为31.6 dB,口径效率为74%,在4.11～4.43 GHz的频带范围内反射小于?16 dB,功率容量3.6 GW。     

波导缝隙阵列天线高功率微波应用探索

设计了一种波导窄边缝隙天线阵,其微波传输工作于行波状态,绝大部分能量被缝隙耦合辐射,其余能量被匹配负载吸收。通过等效电路的方法,使得各个缝隙达到均匀辐射,从而具备可拓展组阵能力,此外通过设计移相结构改变相位差,实现方位角方向的波束扫描。该缝隙天线工作在行波状态,避免了电场集中现象的出现,且工作于真空环境,具有较高的功率容量。     

Nonlinear femtosecond pulse reshaping in waveguide arrays

We observe nonlinear pulse reshaping of femtosecond pulses in a waveguide array owing to coupling between waveguides. Amplified pulses from a mode-locked fiber laser are coupled to an AlGaAs core waveguide array structure. The observed power-dependent pulse reshaping agrees with theory, including shortening of the pulse in the central waveguide.     

Quartz CO2 waveguide laser with a separated diffraction grating

A quartz CO₂ waveguide laser with external totally reflecting mirrors and a NaCl plate for the output power coupling is described. The output power was measured as a function of the distance of the mirrors from the waveguide aperture. Using a diffraction grating instead of one of the mirrors the output power at the 10 P(20) line was measured as a function of the mirror position. The results sustain the assumption of a multimode waveguide structure.     

Ray-optics analysis of the coupling efficiency from a gaussian beam to a rectangular multimode embedded strip waveguide

Abstract

The modified ray-optics method is used to analyze the coupling efficiency from a Gaussian beam to a rectangular multimode embedded strip waveguide. It is convenient for analyzing the case of a simple waveguide structure because of reduced computation time. The conditions for determining which optical rays can be coupled into the waveguide to become the waveguiding modes, as well as the effective receiving area of the waveguide, are derived in this work. The data obtained by this method are compared with those calculated by the well-known overlap integral theorem and Marcatili's models for investigating the validity of the modified ray-optics method.     

Analysis of electrooptically induced waveguides in strontium barium niobate and optical modulators

An electrooptically induced optical waveguide can be formed by applying a DC voltage between electrodes fabricated on the surface of a crystal with strong electrooptic coefficients (for example, strontium barium niobate). Calculations of the refractive index profile and the optical mode size for such waveguides are presented. Approximate solutions for the fundamental mode are used to analyse the power coupling between a single-mode step-profile fibre and these waveguides. The power transmission losses in the straight and S-shaped waveguides are estimated by using a finite-difference beam propagation method (FD-BPM). The calculations predict that a new kind of modulator/switch can be realized with the induced waveguides. The important characteristics of these devices are discussed and compared with LiNbO₃ optical waveguide modulators.     

Loss coefficients for blazed waveguide corrugations

The coupling between bound modes of a corrugated dielectric-slab waveguide and modes of the radiation continuum is analysed by a perturbation method. Loss coefficients that account for the power coupled into radiation modes by any Bragg order of corrugations with an arbitrary profile are determined for the bound modes. Agreement is found with published results for sinusoidal profiles. The proportion of power coupled out through each dielectric interface of the slab waveguide is also determined. When the corrugation has an asymmetric (blazed) profile and coupling to radiation modes is by the first Bragg order, more power can be coupled out through one interface than the other, even if the refractive indices of the cladding regions are equal. If the coupling is by a higher Bragg order, then the division of power can be considerably more unequal than for first-order coupling, with the greater proportion leaving the side of the waveguide opposite to that for first-order coupling. The ratio of the power coupled out the two sides varies cyclically with radiation wavelength.     

Power thresholds of families of discrete surface solitons

We have investigated both theoretically and experimentally the power threshold of discrete Kerr surface solitons at the interface between a discrete one-dimensional (1D) (waveguide array) and a continuous 1D (slab waveguide) AlGaAs medium. Decreasing power thresholds were predicted and measured for soliton trapping at sites with increasing distance from the boundary. The thresholds approached asymptotically the power required for a discrete soliton of equivalent width in an infinite lattice. The minimum threshold coincided with a minimum in the interchannel coupling strength.     

高功率微波波导缝隙阵宽角扫描特性研究

波导间缝隙的互耦会严重降低高功率微波宽边纵缝波导缝隙阵的宽角扫描能力。设计了一L波段高功率宽边纵缝波导缝隙阵,在阵列波导间设计扼流槽结构抑制缝隙互耦。数值模拟结果表明,没有扼流槽结构的阵列波束扫描增益下降3 dB的角度为24.7°,具有扼流结构的阵列扫描增益下降3 dB的角度为33°。同时扼流结构还可以明显改善阵列的有源反射系数,有扼流结构的阵列有源VSWR≤3的带宽为6.6%,而没有扼流结构的阵列有源VSWR≤3的带宽为5.0%。数值模拟结果还表明,波束扫描时(扫描角35°),阵列功率容量可达到957 MW, 比阵列无波束扫描时(1.008 GW)稍低一点。     

Array waveguide evanescent ribbon coupler for card-to-backplane optical interconnects

A flexible array waveguide evanescent coupler for card-to-backplane optical interconnects is presented. The proposed technique eliminates traditional 90 degrees out-of-plane turns and local waveguide termination of multidrop bus architectures that hinder conventional card-to-backplane optical interconnections. Evanescent coupling between array waveguide ribbons has been successfully demonstrated. Further experiments have been performed to quantify array waveguide coupling length versus transfer efficiency and waveguide misalignment tolerance. Preliminary optical interconnect testing has demonstrated 2.5GHz operation of the coupler ribbons. The successful high-speed coupling confirms the effectiveness of the proposed method for high-speed computing systems.     

高功率谐振式波导缝隙阵宽角扫描技术

在传统高功率缝隙波导阵列中,缝隙间的相互耦合严重影响了阵列的宽角扫描能力。以实现阵列宽角波束扫描为目标,通过分析阵列扫描特性,从提高缝隙阵元间隔离度的角度出发,提出在阵列中引入隔离栅结构,降低了阵元间耦合对阵列大角度扫描时的影响。在此基础上,设计了基于波导窄边斜缝的谐振式阵列天线,采用电磁仿真软件优化阵列。数值模拟结果表明,未采取措施前阵列的最大扫描范围为±34°,引入隔离栅后扫描范围可扩大至±45°,波导端口S₁₁≤?10 dB,增益仅下降了2.3 dB,单根缝隙波导功率容量达330 MW,有应用于高功率微波领域的潜质。     

Ray-optics analysis of the coupling efficiency from a gaussian beam to a rectangular multimode embedded strip waveguide

The modified ray-optics method is used to analyze the coupling efficiency from a Gaussian beam to a rectangular multimode embedded strip waveguide. It is convenient for analyzing the case of a simple waveguide structure because of reduced computation time. The conditions for determining which optical rays can be coupled into the waveguide to become the waveguiding modes, as well as the effective receiving area of the waveguide, are derived in this work. The data obtained by this method are compared with those calculated by the well-known overlap integral theorem and Marcatili's models for investigating the validity of the modified ray-optics method.     

Coherent Excitation of X-Ray Fluorescence and Interference of Radiation at the Output of Polycapillary Structures

The diffraction of long-wavelength X rays with the energy corresponding to the region of anomalous dispersion near the Si L_2,3 absorption edges transmitted through microchannel plates has been studied both experimentally and theoretically. The radiation of a finite antenna array, as well as the processes of excitation of X-ray fluorescence and propagation of waves in hollow waveguide structures, has been mathematically simulated. The model describes a polycapillary structure consisting of noninteracting emitters, which are hollow channels of a microchannel plate. It has been shown that coherently excited X-ray fluorescence propagates primarily in the direction of the zeroth diffraction order.     

Output mode characteristics of an in-phase locked gain waveguide array CO2 laser

In this paper,experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO 2 laser are reported.The experimental results of the optical oscillation mode frequency,the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained.A revised mode expression of the rectangle waveguide,which is suited for this waveguide array CO 2 laser,is proposed.The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.     

矩形波导与圆柱波导或圆柱谐振腔间的小孔耦合

本文讨论了三种不同系统的小孔耦合的近似解法:矩形波导与圆柱波导的同轴耦合,矩形波导中的TE₁₀型波与圆柱谐振腔中的TM₁₂₀型波间的耦合和矩形波导中的TE₁₀型波与圆柱波导中的TM_mn型波间的耦合。通过这几个问题的解法,我们希望读者可以看到处理复杂微波元件问题时所需的从物理概念出发的灵活应用已有方法的必要性。这里提供的几个公式有着广泛的应用范围而是在现有文献中探讨得不够的。这里介绍的方法可以应用到其他新的微波网络问题中去。     

Loss analysis and increasing of the fabrication tolerance of resonant coupling by tapering the mode beating section

The film mode matching method was used to analyze the inter waveguide coupling losses in a passive asymmetric twin waveguide caused by waveguide width and refractive index variation for both resonant and adiabatic coupling at a wavelength of 1,550 nm. The reasons for power losses are shown. It is demonstrated that tapering the mode beating section of the resonant coupler can increase the fabrication tolerance of resonant coupling without increasing the coupling length.     

First results with DIAMANT and EUROGAM

The coupling of efficient particle and γ detection arrays is a powerful tool to study the deexcitation of both compound and residual nuclei in fusion evaporation reactions.We show first results obtained coupling the DIAMANT (4π light charged particle array) and EUROGAM (4π γ array) detectors demonstrating the improvement in the resolving power by this combination. For γ rays of ?800keV improvements in the Doppler correction up to 50% have been reached for the 2α exit channel following the fusion of 32S+58Ni at 120 MeV bombarding energy (β ? 3%).