Investigation on the multi-hole directional coupler for power measurement of the J-TEXT ECRH system

Power measurement is necessary for an electron cyclotron resonance heating(ECRH)system.The directional coupler method has been put forward to monitor high-power microwave from gyrotrons in real time.A multi-hole directional coupler has been designed and manufactured for the 105 GHz/500 kW ECRH system on the J-TEXT tokamak.During the design process,we established the relationships between hole parameters and coupling characteristics based on the multi-hole coupling method and small-hole coupling theory.High-power tests have been carried out.The results indicated the reasonability of the theoretical design and practicality of the fabricated directional coupler.Sources of test errors have been discussed in detail,and the influences of spurious modes on the directional couplers have been emphatically analyzed.

Design of a High Power Directional Coupler with High Directivity Used in the LHCD Launcher for EAST

A high power waveguide directional coupler was designed to measure the transmitted power and reflected power in the 4.6 GHz LHCD （lower hybrid current drive） launcher for the EAST tokamak. The design principle of the coupler is assessed. Further analysis is performed by CST （computer simulating test） and Ansoft HFSS （high frequency structure simulator） software and the optimal structural parameter is obtained. In addition, finite element code ANSYS is used to determine the temperature distribution in the coupler conductively cooled by forced water. The test results of a directional coupler manufactured according to the design are close to what is expected.

Fabrication of Polymer Nonlinear Directional Coupler by Photo-bleaching

The preparation of a nonlinear directional coupler in polymer PMMA/DR1 film by photobleaching is studied. We find it easier to obtain a required coupling length by controlling photo bleaching time than by controlling the dimension of the coupler. The transmittance of each arm is measured when the pulse input light energy changes in our experiment. The experimental results show that the coupling length will change with the intensity of input light due to optical nonlinearities of the polymer PMMA/DR1 at 1 064 nm.

Nonideal effects in quantum field-effect directional coupler

The nonideal effects in a quantum field-effect directional coupler where two quantum wires are coupled through a finite potential barrier are studied by adopting the lattice Green function method. The results show that the electron energy distribution, asymmetric geometry and finite temperature all have obvious influence on the electron transfer of the coupler. Only for the electrons with energies in a certain region, can the complete periodic transfer between two quantum wires take place. The conductance of these electrons as a function of the barrier length and potential height exhibits a fine periodic or quasi-periodic pattern. For the electrons with energies beyond the region, however, the complete periodic transfer does not hold any more since many irregular oscillations are superimposed on the conductance profile. In addition, the finite temperature and asymmetric geometry both can reduce the electron transfer efficiency.

The Zero-gap Directional Coupler Integrated on SOI for 1.3μm Operation

SOI zero-gap directional couplers are studied by using large cross-section single-mode rib waveguide theory and dual-mode interference principle in silicon direct bonding SOI by back-polishing. And they are fabricated by using KOH anistropic etching. The insertion loss is measured to 4.81 dB, and the crosstalk is below —18.6 dB at a wavelength of 1.3μm.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric （TE） guided mode and transverse-magnetic （TM） guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguldes is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.Sttm. A finite-difference tlme-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

IMPROVED MODE-MATCHING AND NETWORK ANALYSIS OF E-PLANE WAVEGUIDE BRANCH DIRECTIONAL COUPLERS

The E-plane waveguide branch directional couplers are analyzed by a method which combines the multimode network theory with rigorous mode-matching approach. The electromagnetic field components are expanded by the superposition of LSEx modes rather than TE and TM modes in the mode-matching procedure. Meanwhile, the electromagnetic problem is transferred into the network problem through the mode-matching treatment. It is shown that the present method has the advantages of simplicity and less computation without affecting the accuracy of the calculation.

Analysis and Design of a 3 dB Tunable Lumped-Element Directional Coupler

An analysis of a 3 dB lumped-element directional coupler （LEDC） based on arbitrary terminal impedance is described numerically. To solve the conflicted requirement for broad bandwidth and small size in LEDC, a new structure of coupler is introduced, which can significantly improve bandwidth and whose size is only 3 cm×4 cm on the conditions of the frequency domain of 410 MHz to 490 MHz. The measure results are in good agreement with simulations despite the unexpected resistor loss.

MoM Analysis and Design of a Compact Coaxial-to-Microstrip Directional Coupler

In order to overcome the main drawbacks of coaxial, waveguide, and stripline couplers, the analysis and the design of a compact coaxial-to-microstrip directional coupler convenient for power and antenna control application, are presented using the method of moments (MoM) in two dimensions. This technique is adapted to study the complex configuration of the line’s system, which does not have a simple analytical solution. The modeling of this structure consists in analyzing the primary inductive and capacitive matrices ([L] and [C]). When these matrices are determined, it is possible to calculate the inductive and capacitive coupling coefficients (kL and kC) and estimate the resulting scattering parameters of the coupler using an adapted numerical model. The coupler can be integrated into a printed circuit board (PCB) and operates over 17 to 35 dB coupling coefficients and is always compensated. The compensation is achieved by the proper displacement of a tuning ground plane with respect to the edge of the PCB from 0.1 to 3.3 mm. As an application, we present the design of a compact coupler with 7.5 × 4.8 × 25.8 mm of size and having approximately 20 dB of coupling coefficient at 2 GHz and a minimum directivity of 23.3 dB in the frequency range [0.1 - 4] GHz. In order to check our numerical calculations by the MoM we made simulations in 3D by using CST MICROWAVE STUDIO software for the same geometrical and physical parameters of our designed coupler. The results obtained by the two numerical models (MoM and CST) show a good agreement of the frequency responses of the coaxial-to-microstrip directional coupler. The studied structure represents a great improvement for high power measurement systems, since it has broad-band, good directivity, and can be easily designed and fabricated.

Switching Dynamic Analysis for Twin-Core Fibre Coupler Using Supermode Theory

Characteristics of optical switching in a twin-core fibre coupler are numerically analysed under short pulse input by using supermode theory. The dynamic nonlinear coupled superlnode equations are derived, The numerical results show that the input pulse width determines the power transfer and the pulse temporal profile in the output ports. The optimal switching characteristics can be obtained by selecting an appropriate initial pulse width. In addition, the switching characteristic curves are insensitive to the input pulse shape for either fundamental soliton pulse or Gaussian pulse input, but sensitive to pulse sharpness. A reduced switching power and a sharper switching transition can be obtained by using the sharp super-Gaussian pulse.

Optimization Design and Application of S-Band 3dB Directional Coupler

The application of the 3dB directional coupler is very extensive,such as the phase shifter,the attenuator and the RF pulse compressor etc.The performance of the 3dB directional coupler is very important for these components. Optimization design has been done using the HFSS code.The new phase shifter prototype using the new optimization results has been tested.The tested results are in agreement with the measured ones.

一种宽频带复合天线设计

针对多系统载体天线数量多的问题,提出了一种基于印刷振子结构的宽频带共口径复合天线设计方法;通过两种不同形式的印刷偶极子进行共口径设计:采用平面印刷偶极子结构完成宽带高增益线极化天线,通过宽带定向耦合器实现了天线和差方向图辐射;采用十字印刷偶极子实现低增益天线的圆极化辐射;两种天线单元印刷在同一微波介质上,通过优化天线单元布局,相对位置关系和增加金属隔离环等措施,降低天线之间的相互影响,实现共口径复合天线性能满足工程应用要求;加工了天线样机,测试结果表明线极化天线在工作频带1.2~1.8 GHz范围内和差通道电压驻波比小于1.8,和通道增益大于13.5 dBi,方位差波束零值深度小于-25 dB,圆极化天线在工作频带1.2~1.8 GHz范围内电压驻波比小于1.6,增益大于6.5 dBi,轴比小于2.5 dB,与计算结果基本一致;复合天线可以满足多种无线通信系统的需求,减少了天线数量,有效节省载体平台空间,同时具有结构简单紧凑、剖面低、易于工程实现等特点,具有广阔的应用前景。

太赫兹折叠波导慢波电路及功率合成技术

针对太赫兹频段行波管输出功率较小的瓶颈以及对紧凑型设计的明确需求,提出一种管内功率合成的0.34 THz折叠波导行波管结构。首先,对太赫兹折叠波导慢波结构的高频特性进行了研究,通过仿真计算得到了其色散特性和耦合阻抗,0.34 THz处归一化相速度为0.248,耦合阻抗为0.46Ω;其次,提出了用于管内功率合成的3 dB定向耦合器结构设计,分析表明,其在0.31~0.368 THz范围内,幅度平衡度在±0.19 dB以内,隔离度优于24 dB;最后,完成了基于3 dB定向耦合器管内功率合成的折叠波导行波管基本结构设计并构建了仿真模型,仿真结果表明,最大输出功率为9.16 W,增益为26.6 dB,3 dB带宽达到21 GHz。作为对比,单个折叠波导行波管输出功率为6.18 W,故管内合成的折叠波导行波管的输出功率是单个行波管输出功率的1.48倍;此外,与采用常规外置功率合成结构的双行波管组件设计相比,管内功率合成折叠波导行波管的横向尺寸至少缩减了56.5%。

Broadband directional coupler based on asymmetric dual-core photonic crystal fiber

A novel broadband directional coupler based on an asymmetric dual-core photonic crystal fibet(PCF)is proposed.The asymmetry in the fiher is introduced by the enlargement of one air-hole in dual-core PCF.Numerical investigation demonstrate that broadband directional coupling with spectral width as large as 370 nm and polarization-dependent loss and uniformity lower than 0.2 and 0.5 dB,respectively,can be achieved.In addition,the proposed fiber shows large tolerance to the variation of the fiber parameters.In particular,the fiber length allows at least 10%derivation from the proposed fiber length of 7.7 mm.

大功率超宽带高平坦度定向耦合器设计

宽带大功率射频发射系统中的保护电路需要实时采集准确的射频信号。宽带大功率耦合器作为保护电路的关键器件,其耦合度的平坦度、方向度指标对保护电路采集射频信号的准确性起到关键影响。采用同轴结构的定向耦合器具备极小的插入损耗,在接入射频通路后对通过功率影响极小。通过在拟合网络中采用传输线变压器谐振回路实现宽带高平坦度定向耦合。实测结果表明在80 MHz~1000 MHz频段的5000 W以上量级的大功率定向耦合器中,其耦合度为50 dB时,平坦度≤±0.3 dB,方向度>20 dB,耦合端口电压驻波比(VSWR)≤1.25,主通路插入损耗≤0.1 dB,主通路VSWR≤1.10。

Asymmetric directional couplers based on silicon nanophotonic waveguides and applications

Directional couplers （DCs） have been playing an important role as a basic element for realizing power exchange. Previously most work was focused on symmetric DCs and little work was reported for asymmetric directional couplers （ADCs）. In recently years, silicon nanophotonie waveguides with ultra-high index contrast and ultra-small cross section have been developed very well and it has been shown that ADCs based on silicon-oninsulator （SOI） nanophotonic waveguides have some unique ability for polarization-selective coupling as well as mode-selective coupling, which are respectively very important for polarization-related systems and mode-division-mulitplexing systems. In this paper, a review is given for the recent progresses on silicon-based ADCs and the applications for power splitting, polarization beam splitting, as well as mode conversion/（de）multiplexing.

一种宽频带双圆极化微带天线阵列设计

为了支撑低轨卫星宽带数据下传需求,提出了一款宽频带双圆极化微带天线;采用微带天线作为基本辐射单元,基于层叠寄生贴片方式与加载空气腔方法展宽天线工作带宽并提高增益值,利用电容加载的三分支线定向耦合器对天线单元进行馈电进一步展宽天线带宽,并实现双圆极化辐射特性;单元电性能仿真结果良好,阻抗相对带宽为28.2%,轴比相对带宽达14.5%,峰值增益达到5.6 dBi;基于辐射单元进行4×4阵列组合,所设计阵列天线阻抗带宽覆盖7.7~8.9 GHz,同一单元不同极化与不同单元间端口间隔离度均≥15 dB,轴比在通带内均≤3 dB,方向图仿真与测试结果吻合良好,验证了设计方案的正确性。

A new demodulation technique for optical fiber interferometric sensors with[3×3]directional couplers

Optical fiber interferometric sensors based on [3×3] couplers have been used in many fields. A new technique is proposed to demodulate output signals of this kind of sensors. The technique recovers the signal of interest by fitting coefficients of elliptic （Lissajous） curves between each fiber pair. Different from other approaches, this technique eliminates the dependence on the idealization of [3×3] coupler, provides enhanced tolerance to the variance of photoelectric converters, and is anti-polarization in a certain extent. The main algorithm has been successfully demonstrated both by numerical simulation and experimental result.

High-performance ultra-compact polarization splitterrotators based on dual-etching and tapered asymmetrical directional coupler

High-performance ultra-compact polarization splitter-rotators(PSRs)are designed and experimentally demonstrated,using dual etching and a tapered asymmetrical directional coupler.First,two novel PSRs are designed with nanowire and subwavelength grating cross-port waveguides and verified in simulations.Then,one of the two PSRs is fabricated.Experiment results reveal that the extinction ratio is higher than 28 dB or 32 dB at 1550 nm for the launched fundamental transverse magnetic or the transverse electric modes,while the corresponding insertion loss and polarization conversion loss are 0.33 dB and 0.18 dB,respectively.

Ultra-wideband optical diode based on photonic crystal 90° bend and directional coupler

We propose an ultra-wideband optical diode device based on two-dimensional square-lattice photonic crystals. For the device, the odd mode is completely transmitted in one direction and converted to the fundamental even mode, but completely reflected in the other direction. The operation bandwidth of the device is preserved within a rather wide range of frequencies, which is over 6.5% of the central frequency. A directional coupler and 90° bend are utilized as the composite function device with mode filter and mode converter. It is possible that the photonic crystal device can help to construct on-chip optical logical devices and benefit greatly to the optical systems with multiple spatial modes.