Power switching in hybrid coherent couplers

We report on a theoretical and numerical investigation of the switching of power in new hybrid models of nonlinear coherent couplers consisting of optical slab waveguides with various orders of nonlinearity. The first model consists of two guides with second-order instead of the usual third-order susceptibilities as typified by the Jensen coupler. This second-order system is shown to have a power self-trapping transition at a critical power greater than the third-order susceptibility coupler. Next, we consider a mixed coupler composed of a second-order guide coupled to a third-order guide and show that, although it does not display a rigorous self-trapping transition, for a particular choice of parameters it does show a fairly abrupt trapping of power at a lower power than in the third-order coupler. By coupling this mixed nonlinear pair to a third, purely linear guide, the power trapping can be brought to even lower levels and in this way a satisfactory switching profile can be achieved at less than one sixth the input power needed in the Jensen coupler     

射电天文X波段极化网络一体化设计与研究

射电天文望远镜中极化网络一般由极化器、波导同轴转换器、耦合器等几部分组成,为了获取最高限度的系统灵敏度,极化网络在射电天文低温接收机中会置于低温真空杜瓦20 K 温区,使其对接收机噪声温度的贡献降到最低。通过对极化网络的深入研究设计了一种基于隔板结构的X 波段极化器、耦合器和波导同轴转换器一体化结构。该设计既实现了极化器的线圆转换功能又实现了-30 dB 噪声耦合。测试结果表明该设计拥有良好的轴比、耦合度和驻波特性。同时一体化设计进一步减小了无源器件之间的级联,使低温低噪声放大器之前的馈源网络插入损耗进一步降低,提升了射电望远镜的接收灵敏度。     

利用MWS设计螺旋线行波管耦合结构

利用CST MWS仿真软件对螺旋线行波管耦合结构进行设计.首先,利用MWS仿真结果得出同轴线与螺旋线慢波结构连接部分的反射系数;接着,对高频窗进行了设计与优化;最后,计算出整个耦合结构可能产生的最大驻波系数小于2.0.对比理论值与冷测试数据表明,实测值小于理论计算的最大驻波系数.因此,在螺旋线行波管耦合结构的设计过程中,通过对驻波系数最大值的控制,可以满足实际工程的要求.     

A Variable Directional Coupler Using InSb Thin Films (Short Papers)

A variable directional coupler whose coupling is varied by an applied dc magnetic field is presented in this short paper. The directional coupler is of the two-hole type having InSb thin films in the coupling apertures to which the magnetic field is applied perpendicularly. The directional coupler was tested at room temperature at frequencies from 32 to 36 GHz. At a frequency of 33.1 GHz and magnetic flux densities of up to 13 kG, the coupling varies from 14.2 to 40.2 dB with the directivity exceeding 24.6 dB, the insertion loss of about 1 dB, and the VSWR of 1.2.     

Low-loss monolithic integration of balanced twin-photodetectorswith a 3 dB waveguide coupler for coherent lightwave receivers

Low-loss monolithic integration of a 3-dB waveguide coupler with twin photodetectors using large-mode size guides, mirror coupling, and low-capacitance lateral detectors is demonstrated. Waveguide-mirror integration introduces only ≈1 dB optical insertion loss at 1.54 μm wavelength, compared to top-illuminated detectors. Full balanced operation of the monolithic circuit with 33-dB local oscillator intensity noise suppression is demonstrated     

The Synthesis of N-Port Circulators (Correspondence)

A detector or receiver may be used in conjunction with a directional coupler and a calibrated variable short to measure its own impedance. The observed VSWR as the short is adjusted is the VSWR of the detector if the coupling is light. Various minor corrections are described.     

一种微带功分耦合器的设计

描述了一种微带功分耦合器,它是收发(T/R)组件中的重要组成部分,起着监测和校准的作用.项目设计要求的工作频段在9.3GHz～9.8GHz,端口驻波应小于1.2,两臂间隔离度大于25dB,两个定向耦合器的耦合度C=30dB,定向性D=15dB～20dB.常规微带耦合器的定向性比带状线耦合器的定向性差,有多种方法可以改善...     

Design of a 24-40 GHz balanced low noise amplifier using Lange couplers

A wide band(24-40 GHz)fully integrated balanced low noise amplifier(LNA)using Lange couplers was designed and fabricated with a 0.15/zm pseudomorphic HEMT(pHEMT)technology.A new method to design a low-loss and high-coupling Lange coupler for wide band application in microwave frequency was also presented.This Lange coupler has a minimum loss of 0.09 dB and a maximum loss of 0.2 dB over the bandwidth from 20 to 45 GHz.The measured results show that the realized four-stage balanced LNA using this Lange coupler exhibites a noise figure(NF)of less than 2.7 dB and the maximum gain of 30 dB;moreover,a noticeably improved reflection performance is achieved.The input VSWR and the output VSWR are respectively less than 1.45 and 1.35 dB across the 24-40 GHz frequency range.     

Limitations on power-transfer efficiency in three-guide optical couplers

The eigenvalue equations for a slab three-guide coupler were solved and the power-transfer efficiency was calculated when the coupler is used as 1) a power divider and 2) to transfer power from one outside guide to another. In the first case, two modes take part in the power transfer, and unless the guides are very tightly coupled, periodic beats with high power transfer are obtained at multiples of the coupling length as in a two-guide coupler. In the second case, three modes take part in the power transfer, and periodic beats and high power-transfer efficiency can only be obtained if the propagation velocities of the three modes are related to each other in a simple way. This condition will occur only if the guides of a three-guide coupler made up of identical guides are much more loosely coupled than guides generally used in a two-guide coupler.     

Tapered, both in dimension and in index, velocity coupler: theoryand experiment

The authors consider a tapered velocity coupler (TVC) that meets the adiabatic invariance condition with sufficiently strong coupling between the fundamental modes of individual guides in the middle region of the coupler while permitting individual excitation at the input end and sorting of the modes at the output end. This approach helps reduce the device length considerably by permitting much higher taper angle. A TVC consisting of one tapered and another straight, graded index waveguide is modeled using the normal modes of the entire, composite TVC structure. The analytical results are in excellent agreement with experimental results for a TVC fabricated in Ti:LiNbO₃. It is shown that the representation of the local normal modes as the superposition of the modes of the uncoupled guides leads to erroneous results     

The Design of Interdigitated Couplers for MIC Applications

A straightforward design procedure for microstripline interdigitated directional couplers is outlined. Based on exact, closed-form equations for coupler analysis, a design chart is developed allowing the geometry of the cross section to be found, starting from a prescribed coupling and given bounds on directivity and VSWR. A further chart yields the length of the coupled section once the center-band frequency has been fixed. In this way, a complete picture of coupler performance is made available to the designer so that the necessary tradeoffs between coupling, directivity, and impedance match can be predicted and understood. The accuracy of the design procedure is also discussed in relation with the most important parasitic affecting coupler behavior, such as launching-discontinuity effects and bonding-wire reactances.     

新型圆形槽波导定向耦合器

圆形槽波导是一种新型的高功率毫米波、亚毫米波传输线.为了实现圆形槽波导之间的耦合,本文根据双槽波导的耦合机理,设计出了新型圆形槽波导走向耦合器,并计算了3dB圆形槽波导定向耦合器的频率特性.     

Tunable photonic crystal waveguide coupler with nematic liquid crystals

Photonic crystals (PCs) have great potential in applications for their ability to control lightwave propagation and the possibilities of implementing PC-based optical waveguide into waveguide coupler systems. In this letter, the novel tunable PC waveguide coupler based on nematic liquid crystals is proposed, and its coupling properties are numerically investigated by using the finite-difference time-domain method. The coupling length of PC waveguide couplers with liquid crystals is shorter than the coupling length of coupler without liquid crystals at the same input wavelength. The refractive indexes of liquid crystals can be changed by rotating the directors of liquid crystals. Then, we can control the direction of light propagation in PC waveguide coupler. These results may provide novel application of switching devices in optical circuits.     

Optically Controlled Broadband Millimeter Wave Beam-Splitter-Type Coupler

Recently, Laser-controlled four-port beam-splitter-type couplers with photoinduced plasma layer and band-limited coupling characteristics at millimeter wave frequencies have been proposed for use in dielectric and image guides and circuits. In order to achieve a large dynamic range regarding the optical control of the coupling coefficient narrowband destructive interference in the dark state has been used. In this paper an ultra-broadband coupler for applications at millimeter wave band is proposed. This configuration requires waveguides to be transparent for the optical excitation. Numerical examples for the lowest order modes are presented and discussed considering fused quartz for the dielectric strips of the guides and a 50 μm GaAs film for the active layer.     

基于正交定向耦合器组合的微波功率测量方法

定向耦合器广泛应用于微波系统的功率测量.但定向耦合器的方向隔离度有限,两个方向的耦合输出信号存在一定程度地串扰,影响功率测量的准确性.为了解决这一问题,本文提出一种正交耦合测量方法.该方法采用一对相位差为90°的定向耦合器同时测量功率,通过对测量结果的计算处理,可消除方向串扰的影响.推导了正反向传输功率与正交耦合器组合功率测量值的关系,分析了正交偏差所产生的误差.为了确定耦合器的正交状态,提出了一种准确测量两个定向耦合器之间相位差的方法.实测表明正交耦合方法可有效提高功率和驻波比测量的准确性.     

Analysis and measurement of NRD-guide leaky wave coupler in Ka-band

A new structure for a nonradiative dielectric (NRD) waveguide directional coupler has been developed. The structure combines two NRD guides and a dielectric slab guide in order to utilize a leakage mechanism for coupling. The coupling depends on this leaky mechanism, but not on field interactions as in a conventional proximity coupler. A theoretical formula for calculation of the decay constant is derived. The field along the NRD guide and the decay constant are measured at Ka band (35 GHz) and compared with the theoretical data. Reasonable agreement between the measured and theoretical data is found     

InGaAsP/InP MQW directional coupler switch with small and low-lossbends for fiber-array coupling

We report on a compact InGaAsP/InP MQW directional coupler switch with spacing between the waveguides at the input and the output facets larger than 125 μm, required for the fiber-array coupling, by employing small low-loss bends. The total device length, including both the coupling and the bending regions, with the different optical confinements in the lateral direction is 2 mm. The coupling region of the switch is 420 μm, and the voltage-length product at switching is around 6 Vmm     

Engineering Design Method of Energy Coupler and Impedance Transformer for Millimeter Wave Tubes

The engineering design method of heliz-waveguide and rectangular coupled cavitiy-waveguide energy coupler employed in millimeter wave tubes is described. Experiments show that, the former has broadband matching character )VSWR is less than 2 at 26 - 40GHz). And the later has small reflection (VSWR is less than 1.5 at 34-37.5 GHz). Optimum design method of multi-section and linear taper waveguide impedance transformer is also given in this paper. These impedance transformers can operate at wide frequency range in microwave and millimeter wave band. The design method and examples of couplers and impedance transformers can be referred for tube designers.     

Effects of Second-Order Coupling Coefficient Dispersion on Short-Pulse Propagation and Switching in an Active Two-Core Nonlinear Fiber Coupler

The propagation and switching of short pulses in an active two-core fiber nonlinear directional coupler have been investigated theoretically by using the split-step Fourier method. The analysis highlights the effects of the second-order coupling coefficient dispersion, the linear gain coefficient, and the finite-gain bandwidth on the switching and propagation of short pulses. The research indicates that the linear gain can sharpen the switching characteristic and reduce considerably the switching threshold power, as well as significantly increase the switching efficiency with the influences of the second-order coupling coefficient dispersion. However, both the second-order coupling coefficient dispersion and the finite-gain bandwidth degrade the switching characteristics. In addition, the finite-gain bandwidth of linear gain not only suppresses significantly the pulse compression and amplification caused by the linear gain coefficient, but also suppresses effectively the frequent pulse fluctuation on pulse propagation induced by the second-order coupling coefficient dispersion; consequently, as in the case of the passive fiber coupler, optical pulses tend to restore periodical coupling propagation in active two-core fiber coupler.